slice 8.5: per-agent + per-team level-up endpoints

Level-up analyzes an agent's brain + recent run outcomes (or a
whole team's aggregate state), calls Gemini 2.5 Flash for structured
JSON proposals, and persists them as pending level_up_proposals
rows. Reviewer approves a subset via /apply; the applier commits
only those items.

Migration 0052 adds level_up_proposals (id, workspace_id, agent_id
XOR team_id via CHECK constraint, status, payload JSONB,
applied_items[], model, created_by, approved_by, created_at,
applied_at) + workspace/pending/agent/team indexes.

Rust surface:
  - cm_db::repo::level_up::{insert, get, list_pending, mark_applied,
    mark_rejected}
  - cm_api::level_up::{propose_agent, propose_team, apply}
    Item kinds handled by apply():
      identity_refinement    → UPDATE agents.system_prompt
      skill_add              → agent_skills_ext INSERT
      skill_candidate        → workspace-scoped skills INSERT
                              (deterministic id per (workspace, name))
      brain_consolidation    → set_agent_md on the brain (unlike
                              brain_seed::ingest, this overwrites)
      roster_change / mcp_bundle_change — logged as
                              "not auto-applied, human runs
                              team-wizard" (structural changes need
                              human review of side effects).

API:
  - POST /api/claws/{id}/level-up   → { proposal_id }
  - POST /api/teams/{id}/level-up   → { proposal_id }
  - GET  /api/level-up-proposals    → pending list
  - GET  /api/level-up-proposals/{id}
  - POST /api/level-up-proposals/{id}/apply  { approved_item_ids }
  - POST /api/level-up-proposals/{id}/reject

Uses Gemini 2.5 Flash with response_mime_type: "application/json"
so the model returns structured JSON directly (no ```json fence
stripping needed). Configurable via CLAWMATES_LEVEL_UP_MODEL.

Follow-ups:
  - Frontend diff-review UI (pick items, approve/reject)
  - roster_change / mcp_bundle_change appliers (currently manual)
  - Anthropic + OpenAI proposer variants
  - Promote workspace-scoped skills to builtin via a curator flow

Co-Authored-By: Claude Opus 4.7 <[email protected]>

crates/cm-api/src/routes/mod.rs

@@ -12,6 +12,7 @@ pub mod files;
 pub mod gateway;
 pub mod health;
 pub mod identity;
+pub mod level_up;
 pub mod loops;
 pub mod missions;
 pub mod nodes;