refactor(model): extract compat capability resolver

[luoye520ww]

Summary

• Extracts per-model compatibility capability resolution from the large HTTP model client.
• Keeps existing request body and stream parser behavior unchanged.
• Adds focused tests for provider defaults and per-model endpoint/capability overrides.

Changes

• Adds compat-capabilities.ts as the compatibility capability registry boundary for endpoint format, vision, reasoning, cache usage, tool calling, and max output tokens.
• Routes CompatModelClient endpoint format, reasoning, max-token, and vision checks through the resolver.
• Preserves the legacy default that image forwarding is allowed when no capability resolver is configured.

Tests

• npm.cmd --prefix kun test -- src/adapters/model/compat-capabilities.test.ts src/adapters/model/compat-model-client.endpoint-format.test.ts src/adapters/model/compat-model-client.tool-images.test.ts src/adapters/model/compat-model-client.streaming-tool-calls.test.ts src/adapters/model/compat-model-client.retry.test.ts
• npm.cmd --prefix kun run typecheck
• npm.cmd --prefix kun run build
• git diff --check kunagent/develop...HEAD

[XingYu-Zhong]

Reviewed via Codex triage; approved for merge.