Limit test suite to essential data-loss safeguards and update README

- Remove large/integration test modules that were flaky or non-essential:
  - Delete tests/brain_cli (CLI integration tests) and its __init__.
  - Delete notes_search_client and template_generator test modules.
- Narrow brain_core tests to focus on critical safety checks:
  - Keep only essential config validation (missing DIARY_PATH / PLANNER_PATH).
  - Keep EntryManager/DiaryEntry tests that verify filenames, separate planner path, and basic write/read cycles.
  - Remove many higher-level and integration-style assertions to speed up and stabilize CI.
- Update README Testing section to document the minimal test suite and adjusted coverage summary.

Reason: reduce test noise and flakiness while retaining coverage for operations that could cause data loss or corruption.

Author: madebygps

README.md

@@ -168,13 +168,18 @@ After writing, run `brain diary link today` to add semantic backlinks:
 
 ## Testing
 
+Minimal test suite focused on preventing data loss:
+
 ```bash
 uv run pytest                    # Run all tests
 uv run pytest --cov              # Run with coverage
-uv run pytest tests/brain_core/  # Run specific module
 ```
 
-**Coverage**: 74 tests with 45% overall coverage, 96% on critical paths (plan_commands.py)
+**Coverage**: 7 essential tests covering:
+- Configuration validation (missing paths)
+- File naming (reflection vs. plan entries)
+- Write/read cycles (prevent data loss)
+- Path separation (diary vs. planner)
 
 ## License