refactor(forge): address PR #318 review — PR/Issue split, sqlite state, drop footer

Addresses the five review comments on PR #318:

- Split PullRequest from Issue and add a dedicated read_pr method on
  Forge/ScopedForge/GiteaForge (a PR carries merge state an issue does
  not); is_pr_open now derives from read_pr.
- Replace the JSON-file forge state with a thin swappable CRUD interface
  (ForgeStateStore) backed by SQLite (SqliteForgeStateStore) at
  ~/.bot-bottle/bot-bottle.db.
- Remove the provenance footer (provenance.py + its test): a mutable,
  unsigned PR comment is not an audit record.
- Reword the PRD: provenance is exposed via an API, not surfaced in the
  PR; document the Issue/PullRequest split and the SQLite store.

pyright clean (whole repo), pylint 10/10, 38 forge/resume unit tests pass;
no remaining refs to the removed provenance module or old JSON state API.

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

@@ -9,6 +9,7 @@ from bot_bottle.contrib.forge.base import (
     Forge,
     ForgeScopeError,
     Issue,
+    PullRequest,
     ScopedForge,
 )
 
@@ -23,6 +24,11 @@ class _RecordingForge(Forge):
     def read_issue(self, number: int) -> Issue:
         return Issue(number=number, title="t", body="b", state="open")
 
+    def read_pr(self, number: int) -> PullRequest:
+        return PullRequest(
+            number=number, title="pr", body="b", state="open", merged=False
+        )
+
     def read_comments(self, number: int) -> list[Comment]:
         return [Comment(id=1, user="alice", body="hi")]
 
@@ -52,6 +58,12 @@ class TestScopedForgeReads(unittest.TestCase):
         self.assertEqual(123, self.scoped.read_issue(123).number)
         self.assertEqual("alice", self.scoped.read_comments(500)[0].user)
 
+    def test_read_pr_passes_through(self):
+        pr = self.scoped.read_pr(999)
+        self.assertIsInstance(pr, PullRequest)
+        self.assertEqual(999, pr.number)
+        self.assertFalse(pr.merged)
+
     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"))