VPP LB counters, src-ip-sticky, and frontend state aggregation

New feature: per-VIP / per-backend runtime counters
  * New GetVPPLBCounters RPC serving an in-process snapshot refreshed
    by a 5s scrape loop (internal/vpp/lbstats.go). Each cycle pulls
    the LB plugin's four SimpleCounters (next, first, untracked,
    no-server) plus the FIB /net/route/to CombinedCounter for every
    VIP and every backend host prefix via a single DumpStats call.
  * FIB stats-index discovery via ip_route_lookup (internal/vpp/
    fibstats.go); per-worker reduction happens in the collector.
  * Prometheus collector exports vip_packets_total (kind label),
    vip_route_{packets,bytes}_total, and backend_route_{packets,
    bytes}_total. Metrics source interface extended with VIPStats /
    BackendRouteStats; vpp.Client publishes snapshots via
    atomic.Pointer and clears them on disconnect.
  * New 'show vpp lb counters' CLI command. The 'show vpp lbstate'
    and 'sync vpp lbstate' commands are restructured under 'show
    vpp lb {state,counters}' / 'sync vpp lb state' to make room
    for the new verb.

New feature: src-ip-sticky frontends
  * New frontend YAML key 'src-ip-sticky' (bool). Plumbed through
    config.Frontend, desiredVIP, and the lb_add_del_vip_v2 call.
  * Reflected in gRPC FrontendInfo.src_ip_sticky and VPPLBVIP.
    src_ip_sticky, and shown in 'show vpp lb state' output.
  * Scraped back from VPP by parsing 'show lb vips verbose' through
    cli_inband — lb_vip_details does not expose the flag. The same
    scrape also recovers the LB pool index for each VIP, which the
    stats-segment counters are keyed on. This is a documented
    temporary workaround until VPP ships an lb_vip_v2_dump.
  * src_ip_sticky cannot be mutated on a live VIP, so a flipped flag
    triggers a tear-down-and-recreate in reconcileVIP (ASes deleted
    with flush, VIP deleted, then re-added). Flip is logged.

New feature: frontend state aggregation and events
  * New health.FrontendState (unknown/up/down) and FrontendTransition
    types. A frontend is 'up' iff at least one backend has a nonzero
    effective weight, 'unknown' iff no backend has real state yet,
    and 'down' otherwise.
  * Checker tracks per-frontend aggregate state, recomputing after
    each backend transition and emitting a frontend-transition Event
    on change. Reload drops entries for removed frontends.
  * checker.Event gains an optional FrontendTransition pointer;
    backend- vs. frontend-transition events are demultiplexed on
    that field.
  * WatchEvents now sends an initial snapshot of frontend state on
    connect (mirroring the existing backend snapshot), subscribes
    once to the checker stream, and fans out to backend/frontend
    handlers based on the client's filter flags. The proto
    FrontendEvent message grows name + transition fields.
  * New Checker.FrontendState accessor.

Refactor: pure health helpers
  * Moved the priority-failover selector and the (pool idx, active
    pool, state, cfg weight) → (vpp weight, flush) mapping out of
    internal/vpp/lbsync.go into a new internal/health/weights.go so
    the checker can reuse them for frontend-state computation
    without importing internal/vpp.
  * New functions: health.ActivePoolIndex, BackendEffectiveWeight,
    EffectiveWeights, ComputeFrontendState. lbsync.go now calls
    these directly; vpp.EffectiveWeights is a thin wrapper over
    health.EffectiveWeights retained for the gRPC observability
    path. Fully unit-tested in internal/health/weights_test.go.

maglevc polish
  * --color default is now mode-aware: on in the interactive shell,
    off in one-shot mode so piped output is script-safe. Explicit
    --color=true/false still overrides.
  * New stripHostMask helper drops /32 and /128 from VIP display;
    non-host prefixes pass through unchanged.
  * Counter table column order fixed (first before next) and
    packets/bytes columns renamed to fib-packets/fib-bytes to
    clarify they come from the FIB, not the LB plugin.

Docs
  * config-guide: document src-ip-sticky, including the VIP
    recreate-on-change caveat.
  * user-guide, maglevc.1, maglevd.8: updated command tree, new
    counters command, color defaults, and the src-ip-sticky field.

cmd/maglevc/main.go

@@ -25,9 +25,18 @@ func main() {
 
 func run() error {
 	serverAddr := flag.String("server", "localhost:9090", "maglev server address")
-	color := flag.Bool("color", true, "colorize static labels in output")
+	color := flag.Bool("color", true, "colorize static labels in output (defaults to false in one-shot mode)")
 	flag.Parse()
-	colorEnabled = *color
+
+	// Detect whether -color was explicitly set so we can pick a
+	// mode-aware default: color is useful in the interactive shell but
+	// noise (ANSI escapes) when piping one-shot output into scripts.
+	colorExplicit := false
+	flag.Visit(func(f *flag.Flag) {
+		if f.Name == "color" {
+			colorExplicit = true
+		}
+	})
 
 	conn, err := grpc.NewClient(*serverAddr,
 		grpc.WithTransportCredentials(insecure.NewCredentials()))
@@ -41,13 +50,25 @@ func run() error {
 
 	args := flag.Args()
 	if len(args) == 0 {
-		// Interactive shell: announce version on startup.
+		// Interactive shell: color defaults to true.
+		if colorExplicit {
+			colorEnabled = *color
+		} else {
+			colorEnabled = true
+		}
 		fmt.Printf("maglevc %s (commit %s, built %s)\n",
 			buildinfo.Version(), buildinfo.Commit(), buildinfo.Date())
 		return runShell(ctx, client)
 	}
 
-	// One-shot command from CLI arguments.
+	// One-shot command from CLI arguments: color defaults to false so
+	// output is script-safe. Operators wanting color can still pass
+	// -color=true explicitly.
+	if colorExplicit {
+		colorEnabled = *color
+	} else {
+		colorEnabled = false
+	}
 	root := buildTree()
 	tokens := splitTokens(strings.Join(args, " "))
 	return dispatch(ctx, root, client, tokens)