Dataplane reconcile fixes; LB counters cleanup; SPA scope cookie

Checker / reload:
- Reload's update-in-place branch now mirrors b.Address onto the
  runtime health.Backend. Without this, GetBackend kept returning
  the pre-reload address indefinitely after a config edit that
  touched addresses but not healthcheck settings — the VPP sync
  path reads cfg.Backends directly so the dataplane moved on
  while the gRPC and SPA view stayed wedged on the old IPv4/IPv6.

Sync (internal/vpp/lbsync.go):
- reconcileVIP now detects encap mismatch in addition to
  src-ip-sticky mismatch and takes the full tear-down / re-add
  path via a new shared recreateVIP helper. Triggered when every
  backend flips address family (gre4 <-> gre6) and the existing
  VIP can no longer accept new ASes — previously the sync wedged
  with 'Invalid address family' until a full maglevd restart.
- setASWeight is issued whenever the state machine requests
  flush (a.Flush=true), not only on the weight-value transition
  edge. Fixes the case where a backend reached StateDisabled
  after its effective weight had already been drained to 0 by
  pool failover — the sticky-cache entries pointing at it were
  previously never cleared.

maglev-frontend:
- signal.Ignore(SIGHUP) so a controlling-terminal disconnect
  doesn't kill the daemon.
- debian/vpp-maglev.service grants CAP_SYS_ADMIN in addition to
  CAP_NET_RAW so setns(CLONE_NEWNET) can join the healthcheck
  netns. Comment documents the 'operation not permitted' symptom
  and notes the knob can be dropped if the deployment doesn't use
  the 'netns:' healthcheck option.

LB plugin counters (internal/vpp/lbstats.go + friends):
- Fix the VIP counter regex: the LB plugin registers
  vlib_simple_counter_main_t names without a leading '/'
  (vlib_validate_simple_counter in counter.c:50 uses cm->name
  verbatim; only entries that set cm->stat_segment_name get a
  slash). first/next/untracked/no-server now read through as
  live values instead of zero.
- Drop the per-backend FIB counter block end-to-end (proto,
  grpcapi, metrics, vpp.Client, lbstats, maglevc). Traced from
  lb/node.c:558 into ip{4,6}_forward.h:141 — the LB plugin
  forwards by writing adj_index[VLIB_TX] directly and bypassing
  ip{4,6}_lookup_inline, which is the only path that increments
  lbm_to_counters. The backend's FIB load_balance stats_index
  literally never ticks for LB-forwarded traffic, so the column
  was always zero and misleading. docs/implementation/TODO
  records the full investigation and the recommended upstream
  path (new lb_as_stats_dump API message) for when we're ready
  to carry that VPP patch.
- maglevc show vpp lb counters: plain-text tabular headers.
  label() wraps strings in ANSI escapes (~11 bytes of overhead),
  but tabwriter counts bytes, not rendered width — so a header
  row with label()'d cells and data rows with plain cells drifts
  column alignment on every row. color.go comment now spells
  out the constraint: label() only works when column N is
  wrapped identically in every row (key-value layouts are fine,
  multi-column tables with header-only labelling are not).

SPA:
- stores/scope.ts is cookie-backed (maglev_scope, 1 year,
  SameSite=Lax). App.tsx hydrates from the cookie then validates
  against the fetched snapshots: a cookie referencing a maglevd
  that no longer exists falls through to snaps[0] instead of
  leaving the user on a ghost selection.
- components/Flash.tsx wraps props.value in createMemo. Solid's
  on() fires its callback on every dep notification, not on
  value change — source is right in solid-js/dist/solid.js:460,
  no equality check. Without the memo, flipping scope between
  two 'connected' maglevds (or any other cross-store reactive
  re-eval that doesn't actually change the concrete string)
  replays the animation every time. createMemo's default ===
  dedupe fixes it in one place for every Flash consumer,
  superseding the local createMemo workaround we'd added in
  BackendRow earlier.

internal/vpp/client.go

@@ -66,11 +66,6 @@ type Client struct {
 	// lbStatsLoop. Published as an immutable slice via atomic.Pointer so
 	// Prometheus scrapes (metrics.Collector.Collect) don't take any lock.
 	lbStatsSnap atomic.Pointer[[]metrics.VIPStatEntry]
-
-	// backendRouteSnap is the most recent per-backend FIB stats snapshot
-	// captured by lbStatsLoop. Same atomic-pointer publish pattern as
-	// lbStatsSnap; see logBackendRouteStats in fibstats.go.
-	backendRouteSnap atomic.Pointer[[]metrics.BackendRouteStat]
 }
 
 // SetStateSource attaches a live config + health state source. When set, the
@@ -241,18 +236,6 @@ func (c *Client) VIPStats() []metrics.VIPStatEntry {
 	return *p
 }
 
-// BackendRouteStats satisfies metrics.VPPSource. It returns the latest
-// snapshot of per-backend FIB combined counters (/net/route/to) captured
-// by lbStatsLoop. Returns nil until the first scrape completes, or after
-// a disconnect.
-func (c *Client) BackendRouteStats() []metrics.BackendRouteStat {
-	p := c.backendRouteSnap.Load()
-	if p == nil {
-		return nil
-	}
-	return *p
-}
-
 // VPPInfo satisfies metrics.VPPSource. It returns a copy of the cached
 // connection info as a metrics-local struct so the metrics package doesn't
 // need to import internal/vpp. Second return is false when VPP is not
@@ -309,7 +292,6 @@ func (c *Client) disconnect() {
 	c.lastLBConf = nil // force re-push of lb_conf on reconnect
 	c.mu.Unlock()
 	c.lbStatsSnap.Store(nil)
-	c.backendRouteSnap.Store(nil)
 
 	safeDisconnectAPI(apiConn)
 	safeDisconnectStats(statsConn)