feat(webui): Gitea issue and PR linkage console (Closes #645)

Add a Phase 3 read-only console that resolves issue↔PR linkage with
evidence (closes keyword, branch marker, body mention), surfaces the
latest canonical handoff for a focused thread, and deep-links to Gitea
only under the admin reveal opt-in.

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

webui/app.py

@@ -53,6 +53,11 @@ from webui.session_loader import (
     snapshot_to_dict as session_view_snapshot_to_dict,
 )
 from webui.session_views import render_sessions_page
+from webui.linkage_loader import (
+    load_linkage_snapshot,
+    snapshot_to_dict as linkage_snapshot_to_dict,
+)
+from webui.linkage_views import render_linkage_page
 from webui.inventory import (
     SECTION_NAMES as _INVENTORY_SECTIONS,
     load_inventory_snapshot,
@@ -342,6 +347,41 @@ async def api_sessions(_request: Request) -> JSONResponse:
     return JSONResponse(session_view_snapshot_to_dict(load_session_view_snapshot()))
 
 
+def _linkage_snapshot(request: Request):
+    """Load one linkage snapshot from the request's scope and focus parameters."""
+    return load_linkage_snapshot(
+        request.query_params.get("project") or None,
+        state=request.query_params.get("state"),
+        issue=_query_int(request, "issue"),
+        pr=_query_int(request, "pr"),
+    )
+
+
+async def gitea_linkage(request: Request) -> HTMLResponse:
+    """Gitea issue↔PR linkage console (#645) — read-only.
+
+    Always 200, including on a failed read: this is an operator view, and it
+    must render *why* linkage could not be loaded rather than withhold the page.
+    The snapshot itself carries ``ok=False`` and the page refuses to draw a
+    linkage table it cannot stand behind.
+    """
+    return HTMLResponse(render_linkage_page(_linkage_snapshot(request)))
+
+
+async def api_v1_gitea_linkage(request: Request) -> JSONResponse:
+    """JSON export of the issue↔PR linkage model (#645).
+
+    Unlike the HTML view, the API answers with 502 when the snapshot could not
+    be loaded, so an automated consumer cannot read a fail-closed payload as a
+    successful "no links exist" result.
+    """
+    snapshot = _linkage_snapshot(request)
+    return JSONResponse(
+        linkage_snapshot_to_dict(snapshot),
+        status_code=200 if snapshot.ok else 502,
+    )
+
+
 async def _parse_audit_form(request: Request) -> tuple[str, str | None]:
     if request.method == "GET":
         return "", None
@@ -785,6 +825,8 @@ def create_app(*, bind_host: str | None = None) -> Starlette:
             Route("/api/sessions", api_sessions, methods=["GET"]),
             Route("/api/v1/sessions", api_sessions, methods=["GET"]),
             Route("/api/v1/timeline", api_v1_timeline, methods=["GET"]),
+            Route("/gitea", gitea_linkage, methods=["GET"]),
+            Route("/api/v1/gitea/linkage", api_v1_gitea_linkage, methods=["GET"]),
             Route("/analytics", analytics, methods=["GET"]),
             Route("/api/analytics", api_v1_analytics, methods=["GET"]),
             Route("/api/v1/analytics", api_v1_analytics, methods=["GET"]),