feat(agent): unify models and validate OpenCode providers

Generate chat, task and learning models from agent-models.json.
Use WaterNetwork fast/expert models with 272k context and validate
upstream names before readiness. Add an isolated model check command
with signal-safe cleanup and plugin, Skill and MCP management docs.

Verified in isolation: type checks, 26 focused tests and both model
catalog checks; no model inference requests.

package.json

@@ -13,6 +13,7 @@
     "generate:openapi": "openapi-typescript openapi/openapi.json -o src/generated/server-api.d.ts",
     "check:openapi": "bun run generate:openapi && git diff --exit-code -- openapi/openapi.json src/generated/server-api.d.ts",
     "check": "bun run typecheck && bun run typecheck:opencode",
+    "check:models": "bun scripts/check-models.ts",
     "start": "bun src/server.ts",
     "start:integration:isolated": "bun scripts/start-isolated-integration.ts",
     "start:prod": "bun run check && bun src/server.ts"