slice 3.5a: skills catalog — the "how to think" layer

Introduce the skills catalog: the second half of the two-layer agent
model (skills teach agents HOW to think about a problem; MCP servers
give them the ABILITY to act). Delivery via MCP resources lands in
Slice 3.5b; this slice ships the data model + API surface.

Migration 0049 extends the legacy `skills` table (from 0001_init.sql,
originally a workspace catalog of markdown snippets) with the richer
typing we need — name, when_to_use, tags, source_kind, current_version
— rather than duplicating tables. Also adds:
  - skill_versions       (version history for level-up promotions +
                          rollback; back-pointer via promoted_from
                          JSONB records agent_id / research artifact /
                          brain memory that produced it)
  - template_role_skills (m2m binding skills to team-template roles
                          with pin_in_context + order_idx)
  - agent_skills_ext     (per-agent overlay: include=true adds a skill
                          to the bundle; include=false prunes a
                          template default for this specific agent)

Rust surface:
  - cm_db::repo::skills_catalog with typed Skill/SkillVersion/
    AgentSkillBinding structs + upsert_builtin (idempotent — bumps
    version + appends to skill_versions ONLY when body changes) +
    list_visible/get/get_by_name reads + template + agent binding
    helpers + effective_for_agent (merges template defaults with
    agent overrides, applies exclude precedence, batch-fetches skill
    bodies)
  - cm_api::routes::skills_catalog with:
      GET /api/skills             — list visible
      GET /api/skills/{id}        — detail
      GET /api/claws/{id}/skills  — effective binding (accepts
        template_id + role_slot as query args to merge in template
        defaults)

Follow-ups:
  - Slice 3.5b: clawmates_skills MCP server exposes catalog as MCP
    resources, honoring pin_in_context for auto-injection
  - Slice 3.5c: seed ~40-60 builtin skills across the 6 stacks

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

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

@@ -26,6 +26,7 @@ pub mod research_setup;
 pub mod routines;
 pub mod sessions;
 pub mod skills;
+pub mod skills_catalog;
 pub mod slack;
 pub mod structure;
 pub mod tailscale;