feat(forge): forge library layer for native integration (PRD chunks 1-3, 5)

Implements the bot-bottle side of the forge-native PRD that is
self-contained in this repo (the forge sidecar and orchestrate command
belong to the separate bot-bottle-orchestrator, a PRD non-goal):

- contrib/forge/base.py: Forge ABC + ScopedForge enforcing the
  read-anywhere / write-scoped model (writes rejected outside the
  assigned issue/PRs via ForgeScopeError).
- contrib/gitea/client.py: GiteaClient (stdlib-only HTTP, mirrors the
  deploy-key provisioner) + GiteaForge. Token held by the caller (the
  sidecar), not injected by cred-proxy.
- contrib/gitea/forge_state.py: ForgeState dataclass + atomic
  read/write/delete/all under ~/.bot-bottle/forge/<owner>/<repo>/.
- contrib/gitea/provenance.py: build_provenance_footer — collapsed
  markdown audit footer; watchdog/gitleaks/egress rendering.
- cli/resume.py: `resume --headless --prompt` reusing the shipped
  assume_yes + headless_prompt launch core (the new half of chunk 1).

47 new unit tests; pylint 9.98/10, pyright clean. Forge sidecar (chunk
4), orchestrate command (chunk 6), and forge_env plumbing are deferred:
their only consumer is the separate orchestrator and they are untestable
in isolation here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WL77TgFxKbs3cidGMG9dz7

tests/unit/test_contrib_forge_base.py

@@ -0,0 +1,95 @@
+"""Unit: Forge abstraction + ScopedForge (PRD forge-native-integration)."""
+
+from __future__ import annotations
+
+import unittest
+
+from bot_bottle.contrib.forge.base import (
+    Comment,
+    Forge,
+    ForgeScopeError,
+    Issue,
+    ScopedForge,
+)
+
+
+class _RecordingForge(Forge):
+    """In-memory fake that records writes."""
+
+    def __init__(self) -> None:
+        self.comments: list[tuple[int, str]] = []
+        self.descriptions: list[tuple[int, str]] = []
+
+    def read_issue(self, number: int) -> Issue:
+        return Issue(number=number, title="t", body="b", state="open")
+
+    def read_comments(self, number: int) -> list[Comment]:
+        return [Comment(id=1, user="alice", body="hi")]
+
+    def post_comment(self, number: int, body: str) -> None:
+        self.comments.append((number, body))
+
+    def update_description(self, number: int, body: str) -> None:
+        self.descriptions.append((number, body))
+
+    def is_org_member(self, org: str, username: str) -> bool:
+        return username == "member"
+
+    def get_pr_for_issue(self, number: int) -> int | None:
+        return 99 if number == 17 else None
+
+    def is_pr_open(self, number: int) -> bool:
+        return True
+
+
+class TestScopedForgeReads(unittest.TestCase):
+    def setUp(self) -> None:
+        self.inner = _RecordingForge()
+        self.scoped = ScopedForge(self.inner, assigned_issue=17, assigned_prs=[42])
+
+    def test_reads_pass_through_to_any_number(self):
+        # A number well outside the writable scope still reads fine.
+        self.assertEqual(123, self.scoped.read_issue(123).number)
+        self.assertEqual("alice", self.scoped.read_comments(500)[0].user)
+
+    def test_membership_and_pr_lookups_delegate(self):
+        self.assertTrue(self.scoped.is_org_member("bot-bottle", "member"))
+        self.assertFalse(self.scoped.is_org_member("bot-bottle", "stranger"))
+        self.assertEqual(99, self.scoped.get_pr_for_issue(17))
+        self.assertTrue(self.scoped.is_pr_open(8000))
+
+
+class TestScopedForgeWrites(unittest.TestCase):
+    def setUp(self) -> None:
+        self.inner = _RecordingForge()
+        self.scoped = ScopedForge(self.inner, assigned_issue=17, assigned_prs=[42])
+
+    def test_writable_set_is_issue_plus_prs(self):
+        self.assertEqual(frozenset({17, 42}), self.scoped.writable)
+
+    def test_write_to_assigned_issue_allowed(self):
+        self.scoped.post_comment(17, "done")
+        self.assertEqual([(17, "done")], self.inner.comments)
+
+    def test_write_to_assigned_pr_allowed(self):
+        self.scoped.update_description(42, "new body")
+        self.assertEqual([(42, "new body")], self.inner.descriptions)
+
+    def test_comment_outside_scope_rejected(self):
+        with self.assertRaises(ForgeScopeError) as ctx:
+            self.scoped.post_comment(500, "spam")
+        self.assertIn("500", str(ctx.exception))
+        self.assertEqual([], self.inner.comments)
+
+    def test_description_outside_scope_rejected(self):
+        with self.assertRaises(ForgeScopeError):
+            self.scoped.update_description(500, "tamper")
+        self.assertEqual([], self.inner.descriptions)
+
+    def test_scope_error_is_permission_error(self):
+        # Sidecars can catch the stdlib base type.
+        self.assertTrue(issubclass(ForgeScopeError, PermissionError))
+
+
+if __name__ == "__main__":
+    unittest.main()