chore(comments): address PR #143 review (operator doc, badge test, dedup, type)

- [warn 1] Document the is_agent operator setup so it survives plan deletion:
  added an AI-agent block to .env.example (use a DEDICATED account, set is_agent
  via SQL, never flag a human/shared account) + a CHANGELOG "Added" entry.
- [warn 2] Test the badge deep-link side effects: ai-agent-badge.test.tsx now
  renders inside an explicit jotai store, clicks the badge, and asserts the
  active chat id, window-open, cleared draft, closed history modal, AND that
  stopPropagation keeps a parent onClick from firing.
- [suggestion 3] Hoist the window.matchMedia stub into vitest.setup.ts and drop
  the duplicated beforeAll block from the three test files (ai-agent-badge,
  comment-list-item, role-cards).
- [suggestion 4] Merge the two near-duplicate "non-clickable" cases via it.each.
- [follow-up 6] Introduce a single ProvenanceSource = 'user' | 'agent' type in
  jwt-payload.ts and reference it from AuthProvenanceData, JwtPayload/
  JwtCollabPayload, and resolveSource() — so a typo can't slip through as a bare
  string. (Server auth chain; client IComment mirroring left as a follow-up.)

Follow-up 5 (shared agentSourceFields write-stamp helper) is deferred as the
review marked it — the 6 REST sites use varied shapes (create-spread vs
resolve-conditional-null vs page move), so it's a separate focused refactor.

Tests: client badge/comment/role-cards suites 11/11 pass; server auth+comment
suites 62 pass; typecheck clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.env.example

@@ -123,6 +123,14 @@ MCP_DOCMOST_PASSWORD=
 # expose the port publicly).
 # MCP_TOKEN=
 # MCP_SESSION_IDLE_MS=1800000
+#
+# AI-AGENT ATTRIBUTION (comments/pages written via MCP are badged as "AI"):
+# attribution is driven by a per-user `is_agent` flag on the users row. There is
+# NO admin UI/API for it — set it out-of-band with SQL. Use a DEDICATED service
+# account for the MCP fallback above and flag ONLY that account, e.g.:
+#     UPDATE users SET is_agent = true WHERE email = 'mcp-bot@your-domain';
+# NEVER set is_agent on a human or shared account — every action by that account
+# (including normal human edits) would then be mis-attributed as AI.
 
 # Per-embedding-call timeout in milliseconds for the RAG indexer.
 # A slow/hung embeddings endpoint fails after this and the batch continues.