fix(webui): repair traffic live path contracts for #640 review

Address PR #885 REQUEST_CHANGES: full head_sha pins from queue signals,
reviewer leases keyed by pr_number only, claim inventory via entries,
live-path fixture tests, and traffic state vocabulary docs.

Closes #640 (re-review at new head)

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

webui/lease_loader.py

@@ -182,10 +182,17 @@ def _extract_reviewer_leases(
             parsed = parse_reviewer_lease_comment(comment.get("body") or "")
             if not parsed:
                 continue
+            subject_pr = parsed.get("pr_number") or pr_number
             leases.append(
                 {
                     **parsed,
-                    "pr_number": parsed.get("pr_number") or pr_number,
+                    "pr_number": subject_pr,
+                    # The lease subject is the PR, never the linked issue: a
+                    # reviewer lease on PR #N must not be attributed to issue #N
+                    # or to the issue that PR closes (#640).
+                    "kind": "pr",
+                    "number": subject_pr,
+                    "role": "reviewer",
                     "comment_id": comment.get("id"),
                     "author": (comment.get("user") or {}).get("login"),
                     "created_at": comment.get("created_at"),