Extract sketch assembly MCP tools

[w1ne]

Summary

• move sketch/assembly MCP registry entries into src/agent/mcp/registry/sketchAssemblyTools.ts
• compose that module back into TOOL_REGISTRY at the same slot
• add a public-contract guard for the sketch/assembly slice

Moved tools: solve_sketch, add_constraint, add_part, add_connector, add_mate, add_workspace_target, set_scene_return, solve_mates.

Review

• subagent review: no findings; confirmed no docs/fixtures changed, no import cycle, handlers/metadata/order preserved

Verification

• baseline: focused MCP registry suite passed on origin/develop (7 files / 46 tests)
• red: public contract test failed because ./registry/sketchAssemblyTools did not exist
• npm test -- src/agent/mcp/toolRegistry.publicContract.test.ts
• npm test -- src/agent/mcp/toolRegistry.publicContract.test.ts src/agent/mcp/toolNameConsistency.test.ts tests/integration/mcp/serverToolDispatch.test.ts tests/unit/mcp/toolRegistrySchema.test.ts tests/unit/scripts/distToolNameGate.test.ts tests/unit/skill/skillToolCountDrift.test.ts tests/integration/mcp/listApi.driftSentinel.test.ts
• npm run typecheck
• npx eslint src/agent/mcp/toolRegistry.ts src/agent/mcp/registry/sketchAssemblyTools.ts src/agent/mcp/toolRegistry.publicContract.test.ts