feat: sync model capabilities from OpenRouter API + platform specs

[Slyker]

Summary

Adds automatic model capability synchronization from OpenRouter catalog API + static platform-specs fallback for models exclusive to Groq, Ollama, Pollinations, Cloudflare, and OpenCode.

Changes

New files

• server/src/services/capabilities.ts — 8-strategy findModel() matching engine that syncs context_window, vision, tools, reasoning, and rate limits from OpenRouter /api/frontend/models. Includes PLATFORM_MODEL_SPECS static map for 12 platform-exclusive models and syncPlatformSpecs() for enrichment.
• server/src/tests/services/capabilities.test.ts — 16 unit tests covering all 8 matching strategies.

Modified files

• server/src/db/index.ts — Added syncCapabilities(db) call at boot + supports_reasoning column migration.
• server/src/routes/fallback.ts — Added POST /sync-capabilities endpoint + supports_reasoning and context_window to GET query.
• client/src/pages/FallbackPage.tsx — Added Sync API button, results modal, Reasoning badge, and Context column.
• server/src/tests/db/idempotency.test.ts — Updated expected context_window values for API-synced models.

Test results

• ✅ TypeScript clean (server + client)
• ✅ 360/360 tests pass