feat: add two-layer thinking block validation (proactive + reactive) (#248)

- Add thinking-block-validator hook for proactive prevention before API calls
- Enhance session-recovery to include previous thinking content
- Fix hook registration to actually invoke the validator

Addresses extended thinking errors with Claude Opus/Sonnet 4.5 using tool calls.

Related: https://github.com/vercel/ai/issues/7729
Related: https://github.com/sst/opencode/issues/2599

assets/oh-my-opencode.schema.json

@@ -59,7 +59,8 @@
           "agent-usage-reminder",
           "non-interactive-env",
           "interactive-bash-session",
-          "empty-message-sanitizer"
+          "empty-message-sanitizer",
+          "thinking-block-validator"
         ]
       }
     },