An outside agent files an attributed report of where it got stuck, and the owner sees friction by agent #7658

Part of #7640. Friction from agents like muse and grokbot is invisible because reports are anonymous.

Done when:

• [ ] A report filed with a token (or a signed agent name through OAuth) carries the agent's identity; anonymous still works and says anonymous
• [ ] MCP reports and the reports page group open reports by agent with a count
• [ ] Tests: an attributed report shows its agent; an anonymous one does not claim one; a stranger's text is untrusted

Files: src/core/reports.ts, src/http/api/reports.ts, src/http/mcp/tools/reports.ts, src/web/pages/reports.ts, test/reports-attributed.test.ts

Risks: An agent name given without a token is a claim, not an identity: show it as claimed.

Fits: a builder