feat(journal): outbound trails-to-trails follows (social-federation §6)

Tasks 6.1–6.6. A local user can follow a user on another trails
instance: WebFinger-resolve the handle, verify the target runs
trails.cool via NodeInfo — checked against the ACTOR IRI's host, never
the handle's domain (split-domain constraint) — record a Pending
follow row, deliver a signed Follow. The §4 inbox listeners already
settle (Accept) or drop (Reject) the row.

- federation-outbound.server.ts: followRemoteActor / cancelRemoteFollow
  (Undo delivery) / listOutgoingRemoteFollows. Network steps (lookup,
  NodeInfo, delivery) injectable for offline integration tests.
  Software allowlist: trails-cool.
- /follows/outgoing: follow-by-handle form + pending/accepted list +
  cancel; linked from the feed empty state; i18n en+de. Remote actors
  have no local profile page, so the remote Pending state lives here
  (the profile Pending button from locked accounts covers local).
- /.well-known/trails-cool now publishes software: trails-cool (6.2).
- Clear 4xx codes: invalid_handle, local_handle, remote_resolve_failed,
  not_trails (6.3).
- Tests: handle-parser + allowlist units; integration suite for the
  Pending lifecycle (create/idempotent/refuse-non-trails/refuse-
  unresolvable/own-host/cancel+Undo) with injected network deps; e2e
  anonymous-redirect guard for the new page.

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

packages/i18n/src/locales/de.ts

@@ -321,6 +321,19 @@ export default {
         count_other: "Folgt {{count}}",
         empty: "Folgt noch niemandem.",
       },
+      outgoing: {
+        heading: "Folgen über Instanzen hinweg",
+        subtitle: "Folge Leuten auf anderen trails.cool-Instanzen. Anfragen bleiben ausstehend, bis ihre Instanz sie annimmt.",
+        handleLabel: "Handle der Person",
+        followButton: "Folgen",
+        pendingBadge: "Ausstehend",
+        acceptedBadge: "Folge ich",
+        cancelRequest: "Anfrage zurückziehen",
+        unfollow: "Entfolgen",
+        empty: "Noch keine Follows auf anderen Instanzen. Gib oben ein Handle ein, um zu starten.",
+        notTrails: "Ausgehende Föderation ist derzeit nur zwischen trails-Instanzen möglich — diese Instanz nutzt kein trails.cool.",
+        disabled: "Föderation ist auf dieser Instanz nicht aktiviert.",
+      },
       prevPage: "Zurück",
       nextPage: "Weiter",
       pageOfTotal: "Seite {{page}} von {{totalPages}}",
@@ -328,6 +341,7 @@ export default {
         title: "Feed",
         heading: "Folge ich",
         empty: "Du folgst noch niemandem. Stöbere Profile durch und klicke auf Folgen, um deinen Feed aufzubauen.",
+        followRemote: "Folge jemandem auf einer anderen trails-Instanz →",
         seePublic: "Oder durchstöbere den öffentlichen Feed dieser Instanz →",
         toggle: {
           followed: "Folge ich",

packages/i18n/src/locales/en.ts

@@ -321,6 +321,19 @@ export default {
         count_other: "Following {{count}}",
         empty: "Not following anyone yet.",
       },
+      outgoing: {
+        heading: "Following across instances",
+        subtitle: "Follow people on other trails.cool instances. Requests stay pending until their instance accepts.",
+        handleLabel: "Their handle",
+        followButton: "Follow",
+        pendingBadge: "Pending",
+        acceptedBadge: "Following",
+        cancelRequest: "Cancel request",
+        unfollow: "Unfollow",
+        empty: "No follows on other instances yet. Enter a handle above to start.",
+        notTrails: "Outbound federation is currently trails-to-trails only — that instance doesn't run trails.cool.",
+        disabled: "Federation is not enabled on this instance.",
+      },
       prevPage: "Previous",
       nextPage: "Next",
       pageOfTotal: "Page {{page}} of {{totalPages}}",
@@ -328,6 +341,7 @@ export default {
         title: "Feed",
         heading: "Following",
         empty: "You're not following anyone yet. Browse profiles and tap Follow to start building your feed.",
+        followRemote: "Follow someone on another trails instance →",
         seePublic: "Or browse the instance public feed →",
         toggle: {
           followed: "Following",