The existing /api/combos GET requires a management token, which broke
read-only integrations (opencode-omniroute-auth plugin and similar) that
need to enrich combo capabilities from a normal Bearer API key. Those
clients got 403 AUTH_001 'Invalid management token' even though the same
API key could list models via /v1/models.
This adds GET /v1/combos with the same auth model as /v1/models:
- Accepts valid Bearer API key OR dashboard session cookie.
- Falls back to anonymous when REQUIRE_API_KEY=false (single-user local).
- Projects ONLY public metadata: name, strategy, description, model id,
providerId, comboName (for combo-refs). Internal routing details
(connectionId, weights, labels, sortOrder, config) are stripped.
/api/combos (management writes) is unchanged.
