LB buckets column + health cascade; VPP dump fix; maglevc strictness

SPA (cmd/frontend/web):
- New "lb buckets" column backed by a 1s-debounced GetVPPLBState
  fetch loop with leading+trailing edge coalesce.
- Per-frontend health icon (✅/⚠️/❗/‼️/❓) in the Zippy header,
  gated by a settling flag that suppresses ‼️ until the next lb-state
  reconciliation after a backend transition or weight change.
- In-place leaf merge on lb-state so stable bucket values (e.g. "0")
  don't retrigger the Flash animation on every refresh.
- Zippy cards remember open state in a cookie, default closed on
  fresh load; fixed-width frontend-title-name + reserved icon slot
  so headers line up across all cards.
- Clock-drift watchdog in sse.ts that forces a fresh EventSource on
  laptop-wake so the broker emits a resync instead of hanging on a
  dead half-open socket.

Frontend service (cmd/frontend):
- maglevClient.lbStateLoop, trigger on backend transitions +
  vpp-connect, best-effort fetch on refreshAll.
- Admin handlers explicitly wake the lb-state loop after lifecycle
  ops and set-weight (the latter emits no transition event on the
  maglevd side, so the WatchEvents path wouldn't have caught it).
- /favicon.ico served from embedded web/public IPng logo.

VPP integration:
- internal/vpp/lbstate.go: dumpASesForVIP drops Pfx from the dump
  request (setting it silently wipes IPv4 replies in the LB plugin)
  and filters results by prefix on the response side instead, which
  also demuxes multi-VIP-on-same-port cases correctly.

maglevc:
- Walk now returns the unconsumed token tail; dispatch and the
  question listener reject unknown commands with a targeted error
  instead of dumping the full command tree prefixed with garbage.
- On '?', echo the current line (including the '?') before the help
  list so the output reads like birdc.

Checker / prober:
- internal/checker: ±10% jitter on NextInterval so probes across
  restart don't all fire on the same tick.
- internal/prober: HTTP User-Agent now carries the build version
  and project URL.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/maglevc/tree_test.go

@@ -53,7 +53,7 @@ func TestExpandPathsRoot(t *testing.T) {
 
 func TestExpandPathsShow(t *testing.T) {
 	root := buildTree()
-	showNode, _ := Walk(root, []string{"show"})
+	showNode, _, _ := Walk(root, []string{"show"})
 	lines := expandPaths(showNode, "show", make(map[*Node]bool))
 
 	for _, l := range lines {
@@ -75,7 +75,7 @@ func TestExpandPathsShow(t *testing.T) {
 func TestExpandPathsNoCycles(t *testing.T) {
 	root := buildTree()
 	// watch events has a self-referencing slot; expandPaths must terminate.
-	watchEvents, _ := Walk(root, []string{"watch", "events"})
+	watchEvents, _, _ := Walk(root, []string{"watch", "events"})
 	lines := expandPaths(watchEvents, "watch events", make(map[*Node]bool))
 
 	// Should produce exactly 2 lines: "watch events" and "watch events <opt>".
@@ -87,7 +87,7 @@ func TestExpandPathsNoCycles(t *testing.T) {
 func TestExpandPathsSetBackendName(t *testing.T) {
 	root := buildTree()
 	// Walk to the name slot so displayPrefix carries the actual arg.
-	node, _ := Walk(root, []string{"set", "backend", "mybackend"})
+	node, _, _ := Walk(root, []string{"set", "backend", "mybackend"})
 	lines := expandPaths(node, "set backend mybackend", make(map[*Node]bool))
 
 	want := []string{
@@ -110,31 +110,37 @@ func TestPrefixMatchCollapsedNouns(t *testing.T) {
 	root := buildTree()
 
 	// "sh ba" → show backends (list all) via prefix matching.
-	node, args := Walk(root, []string{"sh", "ba"})
+	node, args, rem := Walk(root, []string{"sh", "ba"})
 	if node.Run == nil {
 		t.Fatal("'sh ba' did not reach a Run node")
 	}
 	if len(args) != 0 {
 		t.Errorf("'sh ba' should have 0 args, got %v", args)
 	}
+	if len(rem) != 0 {
+		t.Errorf("'sh ba' should fully consume tokens, got remaining %v", rem)
+	}
 
 	// "sh ba nginx0" → show backends <name> (get specific) via slot.
-	node, args = Walk(root, []string{"sh", "ba", "nginx0"})
+	node, args, rem = Walk(root, []string{"sh", "ba", "nginx0"})
 	if node.Run == nil {
 		t.Fatal("'sh ba nginx0' did not reach a Run node")
 	}
 	if len(args) != 1 || args[0] != "nginx0" {
 		t.Errorf("'sh ba nginx0' args: got %v, want [nginx0]", args)
 	}
+	if len(rem) != 0 {
+		t.Errorf("'sh ba nginx0' should fully consume tokens, got remaining %v", rem)
+	}
 
 	// "sh fr" → show frontends (list all).
-	node, _ = Walk(root, []string{"sh", "fr"})
+	node, _, _ = Walk(root, []string{"sh", "fr"})
 	if node.Run == nil {
 		t.Fatal("'sh fr' did not reach a Run node")
 	}
 
 	// "sh he icmp" → show healthchecks icmp (get specific).
-	node, args = Walk(root, []string{"sh", "he", "icmp"})
+	node, args, _ = Walk(root, []string{"sh", "he", "icmp"})
 	if node.Run == nil {
 		t.Fatal("'sh he icmp' did not reach a Run node")
 	}
@@ -143,11 +149,37 @@ func TestPrefixMatchCollapsedNouns(t *testing.T) {
 	}
 }
 
+func TestWalkUnknownTokens(t *testing.T) {
+	root := buildTree()
+
+	// A bare unknown word leaves every token unconsumed and anchors
+	// the returned node at the root — callers must treat this as
+	// "unknown command" rather than silently showing the whole tree.
+	node, _, rem := Walk(root, []string{"foo"})
+	if node != root {
+		t.Errorf("'foo' should leave walk at root, got %q", node.Word)
+	}
+	if len(rem) != 1 || rem[0] != "foo" {
+		t.Errorf("'foo' remaining: got %v, want [foo]", rem)
+	}
+
+	// Partial consumption: "show" matches but "bogus" doesn't. The
+	// returned remaining is the first unmatched token onwards so the
+	// caller can point at exactly what was wrong.
+	node, _, rem = Walk(root, []string{"show", "bogus", "tail"})
+	if node.Word != "show" {
+		t.Errorf("'show bogus tail' should stop at show, got %q", node.Word)
+	}
+	if len(rem) != 2 || rem[0] != "bogus" || rem[1] != "tail" {
+		t.Errorf("'show bogus tail' remaining: got %v, want [bogus tail]", rem)
+	}
+}
+
 func TestExpandPathsWeightSlotWalk(t *testing.T) {
 	// Verify the weight command is fully walkable (fixes bug: setWeightValue
 	// and setFrontendPoolName were non-slot nodes that couldn't capture tokens).
 	root := buildTree()
-	node, args := Walk(root, []string{"set", "frontend", "web", "pool", "primary", "backend", "be0", "weight", "42"})
+	node, args, _ := Walk(root, []string{"set", "frontend", "web", "pool", "primary", "backend", "be0", "weight", "42"})
 	if node.Run == nil {
 		t.Fatal("Walk did not reach a Run node for full weight command")
 	}