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/grpcapi/server.go

@@ -375,10 +375,17 @@ func (s *Server) GetVPPLBState(_ context.Context, _ *GetVPPLBStateRequest) (*VPP
 	return lbStateToProto(state), nil
 }
 
-// GetVPPLBCounters returns the most recent per-VIP and per-backend counter
-// snapshot captured by the client's 5s scrape loop. The call is served
-// from an in-process cache and does not hit VPP. An empty response is
-// returned when VPP is disconnected or no scrape has completed yet.
+// GetVPPLBCounters returns the most recent per-VIP counter snapshot
+// captured by the client's 5s scrape loop. The call is served from an
+// in-process cache and does not hit VPP. An empty response is returned
+// when VPP is disconnected or no scrape has completed yet.
+//
+// Per-backend counters are deliberately not included: the LB plugin's
+// forwarding node bypasses the ip{4,6}-lookup path, so the FIB's
+// /net/route/to counter at a backend's stats_index never ticks for
+// LB-forwarded traffic (see internal/vpp/lbstats.go::scrapeLBStats
+// for the full chain). Exposing a zero-valued "packets" column would
+// just mislead operators.
 func (s *Server) GetVPPLBCounters(_ context.Context, _ *GetVPPLBCountersRequest) (*VPPLBCounters, error) {
 	if s.vppClient == nil {
 		return nil, status.Error(codes.Unavailable, "VPP integration is disabled")
@@ -406,17 +413,6 @@ func (s *Server) GetVPPLBCounters(_ context.Context, _ *GetVPPLBCountersRequest)
 		}
 		return out.Vips[i].Port < out.Vips[j].Port
 	})
-	for _, b := range s.vppClient.BackendRouteStats() {
-		out.Backends = append(out.Backends, &VPPLBBackendCounters{
-			Backend: b.Backend,
-			Address: b.Address,
-			Packets: b.Packets,
-			Bytes:   b.Bytes,
-		})
-	}
-	sort.Slice(out.Backends, func(i, j int) bool {
-		return out.Backends[i].Backend < out.Backends[j].Backend
-	})
 	return out, nil
 }