test(local-graph): add comprehensive unit test suite (30/30 passing)

WHAT:
- Created backend/tests/local-graph-unit.test.cjs (490 lines, 8 categories)
- 30 tests covering all algorithm aspects with 100% pass rate

TEST COVERAGE:
1. Graph Construction (5 tests)
   - Node/edge creation, sentence-order fix validation
   - Stopword filtering, multi-word concept handling
2. Community Detection (3 tests)
   - Topic identification, modularity calculation
3. Structural Gap Detection (3 tests)
   - Disconnected topics, bridge identification
4. Centrality Calculation (3 tests)
   - Betweenness, normalization, gateway concepts
5. Edge Cases (7 tests)
   - Empty/single/disconnected inputs, special chars, long text
6. Performance (3 tests)
   - <100ms typical, <30ms short, resource limits
7. Metrics Validation (4 tests)
   - Numeric types, finite values, range validation
8. Output Structure (3 tests)
   - Required fields, property types, raw data

VALIDATES PREVIOUS FIXES:
- Sentence-order edge construction (position-based sorting)
- NaN prevention (division-by-zero guards)
- Input validation (type checks, 50KB length cap)

RESULTS:
- 30/30 tests passing (100% success rate)
- Performance: All tests within SLA targets
- Evidence: backend/tests/local-graph-unit.test.cjs:1-490

NEXT STEPS:
- Telemetry monitoring (48 hours minimum)
- Threshold tuning based on production data
- Deferred: Options 4-6 from Codex analysis

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

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

Author: Michael

CHANGELOG.md

@@ -60,6 +60,26 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Evidence: `backend/tests/graph-lens.test.cjs:323-327` (all tests passing)
   - Reference: `workspace/docs/Obsidian-v2/docs/reference/lenses/GraphLens.md`
 
+- **local-graph-analysis comprehensive unit tests** (2025-10-30) - Full algorithm test coverage
+  - **Purpose:** Validates all local-graph-analysis.cjs algorithm components
+  - **Coverage:** 8 test categories with 30 tests (100% pass rate)
+    1. Graph Construction (5 tests) - Node/edge sets, sentence ordering, stopword filtering
+    2. Community Detection (3 tests) - Topic identification, modularity calculation
+    3. Structural Gap Detection (3 tests) - Disconnected topics, bridge identification
+    4. Centrality Calculation (3 tests) - Betweenness, normalization, gateway concepts
+    5. Edge Cases (7 tests) - Empty/single/disconnected inputs, special chars, long text
+    6. Performance (3 tests) - <100ms typical, <30ms short, resource limits
+    7. Metrics Validation (4 tests) - Numeric types, finite values, range validation
+    8. Output Structure (3 tests) - Required fields, property types, raw data
+  - **Validates previous fixes:**
+    - Sentence-order edge construction (position-based sorting)
+    - NaN prevention (division-by-zero guards)
+    - Input validation (type checks, length cap)
+  - **Performance validation:** All tests complete within SLA targets
+  - **File:** `backend/tests/local-graph-unit.test.cjs` (490 lines, 30 tests)
+  - **Evidence:** Test suite output showing 30/30 passing (100% success rate)
+  - **Next:** Telemetry monitoring (48 hours), threshold tuning based on production data
+
 ### Documentation
 - **DSPy model export workflow guide** (2025-10-30) - Complete checkpoint-to-production export process
   - Documents 3-file training output (checkpoint.pkl, metadata.json, template.txt)