fix(webui): remediate PR #876 REQUEST_CHANGES for analytics (#651)

Address review blockers and medium/low findings:

- F1: HTML-escape all dynamic analytics fields (html.escape quote=True)
- F2: Gate POST /api/v1/analytics/usage through console_authz
  record_analytics_usage (fail closed for unauthenticated / Phase 1)
- F3: Enforce usage_events retention (max rows + max age)
- F4: Coerce None remote/org/repo to empty strings in load_analytics

Add tests for XSS escaping, unauthorized ingest deny, retention, and
None scope coercion. Document authz + retention in analytics guide.

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

task_capability_map.py

@@ -495,6 +495,15 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
         "permission": "gitea.issue.comment",
         "role": "author",
     },
+
+    # #651 console analytics ingest — control-plane DB write, not a Gitea API
+    # call. Authority comes from console RBAC (operator+) plus phase gating;
+    # permission string is a non-Gitea runtime capability so no Gitea profile
+    # can satisfy it by accident.
+    "record_analytics_usage": {
+        "permission": "runtime.record_analytics_usage",
+        "role": "author",
+    },
 }