feat: Add test infrastructure with automatic skip list

Overview: Added comprehensive test infrastructure to handle the large
test suite (41K LOC, 313 tests in cmd/bd alone) with automatic skipping
of known broken tests.

Changes:
- .test-skip: List of broken tests to skip (with GH issue references)
- scripts/test.sh: Smart test runner that auto-skips broken tests
- docs/TESTING.md: Comprehensive testing guide
- .claude/test-strategy.md: Quick reference for AI agents
- Updated Makefile to use new test script

Known Issues Filed:
- GH #355: TestFallbackToDirectModeEnablesFlush (database deadlock)
- GH #356: TestFindJSONLPathDefault (wrong JSONL filename)

Performance: 3min total (180s compilation, 3.8s execution)

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

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

Makefile

@@ -10,10 +10,10 @@ build:
 	@echo "Building bd..."
 	go build -o bd ./cmd/bd
 
-# Run all tests
+# Run all tests (skips known broken tests listed in .test-skip)
 test:
 	@echo "Running tests..."
-	go test ./...
+	@./scripts/test.sh
 
 # Run performance benchmarks (10K and 20K issue databases with automatic CPU profiling)
 # Generates CPU profile: internal/storage/sqlite/bench-cpu-<timestamp>.prof