feat(manifest): trusted agent forge identity and guidance

Implements PRD prd-new-trusted-agent-forge-identity. Moves author identity
and named forge configurations onto the trusted, host-only agent definition,
and lets a bottle repository optionally associate a git-gate repo with one of
the agent's forge aliases.

- Agent-owned identity: new `author` (name/email) and `forge-accounts`
  (alias -> canonical Gitea /api/v1 origin + host `token_secret` ref) on the
  agent manifest. `author` populates the bottle's git user.name/user.email.
- Remove `git-gate.user` from both agents and bottles; fail with a migration
  pointer to `author`. `git-gate` is no longer accepted on an agent.
- Bottle git-gate repos gain optional `forge: <alias>`, resolved against the
  selected agent's forge-accounts at composition (fail-closed on unknown).
- Fail-closed Gitea API URL validation (https, no userinfo/query/fragment,
  /api/v1 base, host lowercased, trailing slash normalized, host dedup).
- Proxy-held credential: synthesize one inspected, token-authenticated egress
  route per referenced forge alias, scoped to the origin + API prefix. The
  token is resolved from the host env at launch into the egress proxy only —
  never the bottle env, prompt, gitconfig, or workspace.
- Generated, non-secret forge workflow guidance appended to the agent prompt
  for associated repos (API base, branch-backed PR flow, AGit-ref prohibition,
  mutation verification); omitted when no repo declares a forge.
- Agents become home-only: cwd `.bot-bottle/agents` no longer contributes,
  overrides, or is selectable; warned-and-ignored like cwd bottles.
- Docs: README examples, PRD 0011 supersession note, manifest schema docstring.
- Tests: new test_forge_identity suite; legacy git-gate.user/cwd tests updated
  to the agent-owned identity model.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/egress/__init__.py

@@ -32,6 +32,7 @@ if TYPE_CHECKING:
         EGRESS_ROUTES_IN_CONTAINER,
         Egress,
         egress_agent_env_entries,
+        egress_forge_routes,
         egress_gateway_env_entries,
         egress_manifest_routes,
         egress_render_routes,
@@ -51,6 +52,7 @@ _LAZY: dict[str, str] = {
     "EGRESS_ROUTES_FILENAME": ".service",
     "EGRESS_ROUTES_IN_CONTAINER": ".service",
     "egress_agent_env_entries": ".service",
+    "egress_forge_routes": ".service",
     "egress_gateway_env_entries": ".service",
     "egress_manifest_routes": ".service",
     "egress_render_routes": ".service",
@@ -80,6 +82,7 @@ __all__ = [
     "Egress",
     "EgressPlan",
     "EgressRoute",
+    "egress_forge_routes",
     "egress_manifest_routes",
     "egress_render_routes",
     "egress_resolve_token_values",