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_gitea_client.py

@@ -126,6 +126,20 @@ class TestPRHelpers(unittest.TestCase):
         with patch(_URLOPEN, return_value=_resp({"state": "closed"})):
             self.assertFalse(GiteaForge(_client()).is_pr_open(18))
 
+    def test_read_pr_maps_fields_including_merged(self):
+        raw = {"number": 18, "title": "Fix", "body": "patch",
+               "state": "closed", "merged": True}
+        with patch(_URLOPEN, return_value=_resp(raw)) as m:
+            pr = GiteaForge(_client()).read_pr(18)
+        self.assertEqual((18, "Fix", "patch", "closed", True),
+                         (pr.number, pr.title, pr.body, pr.state, pr.merged))
+        self.assertIn("/repos/didericis/bot-bottle/pulls/18",
+                      m.call_args.args[0].full_url)
+
+    def test_read_pr_merged_defaults_false(self):
+        with patch(_URLOPEN, return_value=_resp({"number": 18, "state": "open"})):
+            self.assertFalse(GiteaForge(_client()).read_pr(18).merged)
+
 
 if __name__ == "__main__":
     unittest.main()