feat(journal): federation protocol doc + delivery observability

Task group 4 of federation-hardening.

4.1 — FEDERATION.md at the repo root: actor discovery (WebFinger, actor,
NodeInfo), object/activity types with real JSON examples (Note, Create,
Delete, the narrow follow-graph inbox), addressing, HTTP-Signature
expectations, the two-layer dedup contract, durable delivery/retry
policy, and blocklist moderation semantics — precise enough for another
implementation to interoperate. Linked from README and docs/architecture.

4.2 — three prom-client metrics + a journal dashboard row:
- `federation_delivery_total{outcome}` — incremented in deliver-activity
  (delivered/skipped/failed).
- `federation_inbox_dropped_total{reason}` — incremented at every inbox
  drop (duplicate | blocked); this is the counter deferred from task 3.2.
- `federation_queue_depth` — gauge sampled at scrape time in
  /api/metrics from PgBossMessageQueue.getDepth(); the restart-loss
  regression detector.
Grafana journal.json gains a Federation row (delivery rate, queue depth,
inbox drops); the logs panels shift down to make room.

Verified: dashboard JSON valid; journal typecheck + lint clean; unit
suite 357 passing (route-template guard unaffected).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/journal/app/lib/metrics.server.ts

@@ -48,6 +48,42 @@ export const demoBotSyntheticActivitiesTotal = getOrCreate(
     }),
 );
 
+// --- Federation metrics (spec: federation-operations "Federation delivery
+// observability") ---------------------------------------------------------
+
+/** Outbound delivery attempts by outcome (delivered | skipped | failed). */
+export const federationDeliveryTotal = getOrCreate(
+  "federation_delivery_total",
+  () =>
+    new client.Counter({
+      name: "federation_delivery_total",
+      help: "Outbound federation delivery attempts by outcome",
+      labelNames: ["outcome"] as const,
+    }),
+);
+
+/** Inbound activities dropped, by reason (duplicate | blocked). */
+export const federationInboxDroppedTotal = getOrCreate(
+  "federation_inbox_dropped_total",
+  () =>
+    new client.Counter({
+      name: "federation_inbox_dropped_total",
+      help: "Inbound federation activities dropped before side effects, by reason",
+      labelNames: ["reason"] as const,
+    }),
+);
+
+/** Messages waiting in the durable Fedify queue. Set at scrape time by the
+ * metrics route (the restart-loss regression detector). */
+export const federationQueueDepth = getOrCreate(
+  "federation_queue_depth",
+  () =>
+    new client.Gauge({
+      name: "federation_queue_depth",
+      help: "Messages waiting in the durable Fedify (pg-boss) message queue",
+    }),
+);
+
 export const registry = client.register;
 
 // --- Route label normalization -------------------------------------------