feat: enforce issue-linked branches + document versioning/tagging policy (#48)

Formalize the branch↔issue relationship and add a release/version-tagging policy.

Branch/issue linkage:
- scripts/worktree-start now validates branch names: implementation branches
  must match (fix|feat|docs|chore)/issue-<number>-<slug>; review branches
  review/pr-<number>-<slug>. Untraceable names are rejected with a clear error
  (exit 2). New --allow-unlinked override for genuine exceptions. --dry-run
  preserved.
- Documented issue → branch → worktree → PR → cleanup traceability in the
  runbook and the portable SKILL, including the claim-comment convention and
  Closes #n / Refs #n PR-body usage.
- Noted that Gitea exposes no native issue→branch API field (only a PR head
  branch), so linkage is enforced via branch name + claim comment + PR body +
  cleanup.

Versioning / tagging policy (docs only; no release automation yet):
- SemVer vMAJOR.MINOR.PATCH (v0.x.y while unstable) with PATCH/MINOR/MAJOR bump
  rules.
- Annotated tags only, from the exact commit on remote master, only after the
  full suite passes, with release notes referencing merged PRs/issues. Never tag
  feature branches, dirty worktrees, unreviewed/self-authored work, or commits
  not on remote master.
- Release runbook in the runbook + SKILL, plus a new
  skills/llm-project-workflow/templates/release-tag.md prompt template.

Tests: worktree-start branch validation — accepts fix/feat/docs/chore/issue-*
and review/pr-*, rejects fix/random-name / my-branch / non-numeric issue,
honors --allow-unlinked, preserves --dry-run. Full suite 291 passed / 0 failures;
bash -n clean; git diff --check clean; no secrets.

Release-tag automation (a scripts/release-tag helper) intentionally deferred to a
later issue to keep this diff narrow and testable.

Closes #48. Refs #38, #39, #46.

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

tests/test_worktrees.py

@@ -35,16 +35,43 @@ class TestWorktreeStart(unittest.TestCase):
         self.assertEqual(rc, 2)
 
     def test_refuses_existing_worktree(self):
-        slug = f"zz-refuse-start-{os.getpid()}"
+        branch = f"fix/issue-999-refuse-{os.getpid()}"
+        slug = branch.replace("/", "-")
         target = BRANCHES / slug
         target.mkdir(parents=True, exist_ok=True)
         try:
-            rc, _, err = run("worktree-start", "--dry-run", slug)
+            rc, _, err = run("worktree-start", "--dry-run", branch)
             self.assertEqual(rc, 1)
             self.assertIn("Refusing to reuse", err)
         finally:
             target.rmdir()
 
+    # -- issue-linked branch validation (#48) --------------------------------
+
+    def test_accepts_issue_linked_impl_branches(self):
+        for branch in ("fix/issue-123-example", "feat/issue-123-example",
+                       "docs/issue-123-example", "chore/issue-123-example"):
+            rc, out, err = run("worktree-start", "--dry-run", branch)
+            self.assertEqual(rc, 0, f"{branch}: {err}")
+            self.assertIn(f"branches/{branch.replace('/', '-')}", out)
+
+    def test_accepts_review_branch(self):
+        rc, out, _ = run("worktree-start", "--dry-run", "review/pr-456-example")
+        self.assertEqual(rc, 0)
+        self.assertIn("branches/review-pr-456-example", out)
+
+    def test_rejects_untraceable_branches(self):
+        for branch in ("fix/random-name", "my-branch", "feat/no-issue-here",
+                       "fix/issue-abc-x"):
+            rc, _, err = run("worktree-start", "--dry-run", branch)
+            self.assertEqual(rc, 2, branch)
+            self.assertIn("Untraceable branch name", err)
+
+    def test_allow_unlinked_override(self):
+        rc, out, _ = run("worktree-start", "--dry-run", "--allow-unlinked", "my-branch")
+        self.assertEqual(rc, 0)
+        self.assertIn("branches/my-branch", out)
+
 
 class TestWorktreeReview(unittest.TestCase):