fix: strip cache_control fields from content blocks (#189)

Claude Code CLI sends cache_control on text, thinking, tool_use, and
tool_result blocks for prompt caching. Cloud Code API rejects these
with "Extra inputs are not permitted".

- Add cleanCacheControl() to proactively strip cache_control at pipeline entry
- Add sanitizeTextBlock() and sanitizeToolUseBlock() for defense-in-depth
- Update reorderAssistantContent() to use block sanitizers
- Add test-cache-control.cjs with multi-model test coverage
- Update frontend dashboard tests to match current UI design
- Update strategy tests to match v2.4.0 fallback behavior
- Update CLAUDE.md and README.md with recent features

Inspired by Antigravity-Manager's clean_cache_control_from_messages() pattern.

Co-Authored-By: Claude <noreply@anthropic.com>

tests/run-all.cjs

@@ -10,6 +10,7 @@ const path = require('path');
 
 const tests = [
     { name: 'Account Selection Strategies', file: 'test-strategies.cjs' },
+    { name: 'Cache Control Stripping', file: 'test-cache-control.cjs' },
     { name: 'Thinking Signatures', file: 'test-thinking-signatures.cjs' },
     { name: 'Multi-turn Tools (Non-Streaming)', file: 'test-multiturn-thinking-tools.cjs' },
     { name: 'Multi-turn Tools (Streaming)', file: 'test-multiturn-thinking-tools-streaming.cjs' },