chore: release v2.15.2 with 100% test coverage

- Bump version to 2.15.2
- Add comprehensive changelog entry documenting all improvements
- Add 31 new unit tests achieving 100% coverage for changed code
- Fix flaky integration tests with deterministic ordering

Test Coverage Improvements:
- buildMetadataFilterConditions: All filter combinations (11 tests)
- Performance logging validation (3 tests)
- ID filtering edge cases (7 tests)
- getMetadataSearchCount: Shared helper usage (7 tests)
- Two-phase optimization verification (3 tests)

Coverage increased from 36.58% to 100% for patch

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.15.1",
+  "version": "2.15.2",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "bin": {