feat(agents): markdown agent definitions with unified editor

[hyldmo]

Merges delegated roles and Auto-routing profiles into one canonical store: a directory of Markdown agent-definition files with YAML-style frontmatter (stateDir()/agents/*.md), matching the .claude/agents format, plus one editor for both.

Store (1f77d99)

• One file per agent: frontmatter description / model / effort / fast / routing, body = delegation preamble. Unknown frontmatter (e.g. tools: from imported Claude definitions) is preserved byte-for-byte through every rewrite; no YAML dependency.
• routing.json holds the Auto globals (defaultAuto, router, fallback, rules, timeout). Auto profiles are now derived: any agent with a description and routing != false is routable, so a role and its routing profile can no longer drift apart.
• Copy-only migration from roles.json + auto-model.json (staged dir + single rename, concurrent-safe); legacy files are never rewritten, so an older installed relay sharing the stateDir keeps working.
• New GET/PATCH /api/agents and GET/PATCH /api/routing; the four legacy routes (/api/roles, /api/auto-model) stay as compat adapters over the new store, so MCP list_roles and cached PWAs keep working.

Unified editor (f4e54fd)

• One single-scroll Agents sheet replaces RolesSettings and AutoModelSettings: agent cards (model/effort/fast, routing description, preamble disclosure) with the Auto-routing section below.
• All three entry points open it; the model-picker gear deep-links to the routing section. Fallback agent is protected from removal/un-routing until a replacement is saved; partial saves are reported and retry only the unsaved half.

Import (804bd20)

• Import from ~/.claude/agents in the sheet: bounded scan (64 files, 256 KiB cap), symlink/TOCTOU/UTF-8 hardening, per-name outcomes, explicit overwrite. Imported files keep their bytes exactly; native model aliases (haiku) surface as picker-validation errors on the card instead of importing blind.

yarn verify: 162 test files, 1336 tests.

🤖 Generated with Claude Code