Bug fixes, config validation, SPA tightening, set-weight UI

This session covers three distinct arcs: correctness bug fixes in the
VPP sync path and frontend reducers, new config validation, and a
large polish pass on the web frontend (tighter layout, backend kebab
dialogs, live grouped-table, live config-reload re-sync).

 - encap for a VIP is now derived from the backend address family,
   not the VIP's. A v6 VIP with v4 backends is programmed as IP6_GRE4
   (not the buggy IP6_GRE6), matching the VPP LB plugin's
   requirement that encap reflects the tunnel inner family. desiredVIP
   gained an Encap field populated in desiredFromFrontend.
 - ActivePoolIndex now requires at least one backend in a pool to be
   BOTH in StateUp AND pb.Weight>0 before the pool counts as active.
   Previously a primary pool with every backend manually zeroed would
   still win over a fallback with weight=100, so fallback traffic
   never materialized. New TestActivePoolIndexWeightedFailover table
   pins the rule in five subcases.
 - SyncLBStateVIP gained a flushAddress parameter threaded through
   reconcileVIP; it forces flush=true on the setASWeight call for a
   specific backend regardless of the usual 0→N heuristic. Wires up
   the explicit [flush] knob the CLI exposes.

 - convertFrontend already enforced that backends within one frontend
   share a family. New cross-frontend pass validateVIPFamilyConsistency
   rejects configs where two frontends share a VIP address but carry
   backends in different families — VPP's LB plugin requires every
   VIP on a prefix to have the same encap type, so such a config
   would fail at lb_add_del_vip_v2 time with VNET_API_ERROR_INVALID
   _ARGUMENT (-73). Catching it at config load turns a silent
   runtime failure into a clear startup error.
 - Two new TestValidationErrors cases pin the behavior: mismatched
   families reject, same-family frontends on one VIP address allowed.

 - Proto adds `bool flush = 5` to SetWeightRequest. The RPC now
   drives a VIP sync immediately after mutating config (fixing the
   latent "weight change only takes effect at the next 30s periodic
   reconcile" gap), passing flushAddress = backend IP when req.Flush
   is true.
 - maglevc grows an optional [flush] token: `set frontend F pool P
   backend B weight N [flush]`. Implementation uses two Run closures
   (runSetFrontendPoolBackendWeight and -Flush) because the tree
   walker only puts slot tokens in args — literal keywords like
   `flush` advance the node but don't appear in the arg list.
 - docs/user-guide.md updated with the [flush] optional and a
   three-paragraph explainer of the graceful-drain vs. flush
   semantics at the VPP level.

 - checker.ListFrontends now sorts alphabetically to match the
   existing sort in ListBackends / ListHealthChecks — RPC responses
   no longer shuffle VIPs per call. cmd/frontend/client.go also
   sorts defensively in refreshAll so an old maglevd build renders
   alphabetically too.
 - backendFromProto was returning out.Transitions[n-1] as the
   LastTransition, but maglevd stores (and the proto carries)
   transitions newest-first, so [n-1] was actually the oldest.
   Reverse on read, which normalizes the client's Transitions slice
   to oldest-first and makes [n-1] genuinely the newest. LastTransition
   now points at the actual latest transition record.
 - applyBackendTransition (Go and TS) derives Enabled = state!="disabled"
   so the two fields stay in lockstep — closed a drift window where
   a recently re-enabled backend still rendered with a stuck
   [disabled] tag. The tag was later removed entirely since state
   and enabled carry the same information.

 - Layout tightened substantially: "FRONTENDS" panel header removed,
   zippy-summary and zippy-body paddings cut, backend-table row
   padding dropped to 2px, per-pool <h3> removed. Pools now live in
   a single consolidated table per frontend with a dedicated "pool"
   column that shows the pool name only on the first row of each
   group — classic grouped-table layout, maximally dense.
 - Description moved inline into the Zippy summary as muted italic
   text, freeing a vertical line per frontend card.
 - formatVIPAddress() helper renders IPv6 VIPs as [addr]:port and
   IPv4 as addr:port, matching RFC 3986 authority syntax.
 - Pools with effective_weight=0 on every backend (standby
   fallbacks, fully-drained primaries) render at opacity 0.35 on
   their non-actions cells; the kebab column stays at full contrast
   because its menu is still fully functional on standby backends.
 - Config-reload propagation: a maglevd config-reload-done log
   event triggers triggerConfigResync() on the frontend side —
   refreshAll() runs off the event-dispatch goroutine, then a
   BrowserEvent{Type:"resync"} is published through the broker.
   writeEvent emits type="resync" as a named SSE frame so the
   SPA's existing addEventListener("resync") handler picks it up
   and calls fetchAllState → replaceAll.
 - recomputeEffectiveWeights in stores/state.ts mirrors the
   server-side health.EffectiveWeights logic so the SPA keeps
   pool.effective_weight correct the moment a backend transitions,
   without waiting for the 30s refresh. Fixed a nasty bug where
   applyBackendEffectiveWeight wrote VIP-scoped vpp-lb-sync-as-*
   event weights into every frontend sharing the backend,
   corrupting frontends with different per-pool configured weights.
   The old log-event reducer was removed; applyConfiguredWeight is
   the narrower replacement used by the kebab set-weight flow.
 - applyBackendTransition calls recomputeEffectiveWeights after
   state updates so pool-failover transitions (primary ⇌ fallback)
   reflect instantly in the UI.

 - Confirmation dialogs via a new Modal primitive
   (Portal-mounted to document.body, escape/click-outside close,
   click-outside debounced on mousedown so mid-row-text-selection
   drags don't dismiss).
 - pause/resume/enable/disable each show a Modal with a consequence
   paragraph explaining what hits live traffic ("will keep existing
   flows", "will flush VPP's flow table", etc.). The disable commit
   button is styled btn-danger red.
 - set-weight action shows a Modal with a range slider (0-100,
   seeded from the current configured weight, accent-colored live
   numeric readout via <output>) plus a flush checkbox and a live-
   swapping note/warn paragraph describing what will happen. On
   commit, the SPA also updates its local store via
   applyConfiguredWeight so the operator sees the new weight
   immediately without waiting for the next refresh.

 - ProbeHeartbeat is now state-aware: ▶ (play) at rest for up/
   down/unknown backends, ⏸ (pause) for paused, ⏹ (stop) for
   disabled/removed, ❤️ (heart) during an in-flight probe.
 - Drop the probe-done event listener — fast probes (<10ms)
   could fire probe-done in the same render tick as probe-start
   and the heart would never visibly paint. Each probe-start now
   runs a fixed 400ms scale-pop animation on a timer; subsequent
   probe-start events reset the timer, so fast cadences produce a
   continuous heart pulse.
 - Fixed wrapper box (16x14 px, overflow hidden) so the row
   doesn't jiggle when the glyph swaps between the narrow ▶/⏸/⏹
   text glyphs and the wider ❤️ emoji.

 - Brand wordmark changed from "maglev" to "vpp-maglev" and wrapped
   in an <a> linking to https://git.ipng.ch/ipng/vpp-maglev. Logo
   link changed to https://ipng.ch/. Both open in a new tab with
   rel="noopener".
 - .gitignore fix: `frontend`, `maglevc`, `maglevd` were matching
   ANY file or directory with those names anywhere in the tree,
   silently ignoring cmd/frontend and friends. Anchored with
   leading slashes so only repo-root build artifacts match.

.gitignore

@@ -6,3 +6,9 @@ tests/.venv/
 tests/**/maglevd.log
 tests/**/clab-*/
 cmd/frontend/web/node_modules/
+# Binaries built at the repo root via `go build ./cmd/<name>/` (no -o).
+# Anchored with a leading slash so they don't also match the source
+# dirs under cmd/.
+/frontend
+/maglevc
+/maglevd