feat: add MCP server config + MCP tools for Pi/CCSDK

…us-4.6 to Copilot models

- Add normalizeBraveLang() to map bare 'zh' to 'zh-hans' for Brave Search API (openclaw#64)
- Update GitHub Copilot model list with full catalog including claude-opus-4.6 (openclaw#59)
- resolveImplicitCopilotProvider now provides complete model definitions
- Add unit tests for language normalization

Closes openclaw#64, Closes openclaw#59

Co-Authored-By: Warp <agent@warp.dev>

- Add limitHistoryByTokenBudget() function with sliding window approach
- Integrates after turn-based limiting to enforce token count ceiling
- Default 12,000 token budget (conservative for system prompt + response)
- Graceful error handling: falls back to full history if estimation fails
- Safety guarantee: always keeps at least the last message

Config integration:
- Add agents.defaults.promptTokenBudget config option (optional)
- Reads from params.config?.agents?.defaults?.promptTokenBudget
- Uses estimateTokens() from @mariozechner/pi-coding-agent

Files modified:
- src/agents/pi-embedded-runner/history.ts: new limitHistoryByTokenBudget()
- src/agents/pi-embedded-runner/compact.ts: integrate token budget limiting
- src/config/types.agent-defaults.ts: add promptTokenBudget config type
- src/agents/pi-embedded-runner.limithistorybytoken-budget.test.ts: test coverage

Fixes #59

- Add Zod schema validation for agents.defaults.promptTokenBudget
- Allows runtime config validation to accept the new optional field
- Completes Issue #59 implementation (missing validation schema)

Related to: 0df4ce6

Add Recording Overlay

…udgets (#76 #75 #59)

…ne-green

chore(ci): restore green checks (format, protocol gen, ui typecheck)