Add tests for getMultiRepoJSONLPaths() edge cases

From bd-xo6b code review: Missing test coverage for getMultiRepoJSONLPaths() edge cases.

Current test gaps:
- No tests for empty paths in config
- No tests for duplicate paths
- No tests for tilde expansion
- No tests for relative paths
- No tests for symlinks
- No tests for paths with spaces
- No tests for invalid/non-existent paths

Test cases needed:

1. Empty path handling:
   Primary = empty, Additional = [empty]
   Expected: Should either use . as default or error gracefully

2. Duplicate detection:
   Primary = ., Additional = [., ./]
   Expected: Should return unique paths only

3. Path normalization:
   Primary = ~/repos/main, Additional = [../other, ./foo/../bar]
   Expected: Should expand to absolute canonical paths

4. Partial failure scenarios:
   What if snapshot capture succeeds for repos 1-2 but fails on repo 3?
   Test that system does not end up in inconsistent state

Files:
- cmd/bd/deletion_tracking_test.go (add new tests)

Dependencies:
Depends on fixing getMultiRepoJSONLPaths() path normalization first.


SearchIssues N+1 query causes context timeout with GetLabels

scanIssues() calls GetLabels in a loop for every issue, causing N+1 queries and context deadline exceeded errors when used with short timeouts or in-memory databases. This is especially problematic since SearchIssues already supports label filtering via SQL WHERE clauses.


Audit Current Cache Usage

Understand exactly what code depends on the storage cache

AUDIT COMPLETE

getStorageForRequest() callers: 17 production + 11 test
- server_issues_epics.go: 8 calls
- server_labels_deps_comments.go: 4 calls
- server_export_import_auto.go: 2 calls
- server_compact.go: 2 calls
- server_routing_validation_diagnostics.go: 1 call
- server_eviction_test.go: 11 calls (DELETE entire file)

Pattern everywhere: store, err := s.getStorageForRequest(req) → store := s.storage

req.Cwd usage: Only for multi-repo routing. Local daemon always serves 1 repo, so routing is unused.

MCP server: Uses separate daemons per repo (no req.Cwd usage found). NOT affected by cache removal.

Cache env vars to deprecate:
- BEADS_DAEMON_MAX_CACHE_SIZE (used in server_core.go:63)
- BEADS_DAEMON_CACHE_TTL (used in server_core.go:72)
- BEADS_DAEMON_MEMORY_THRESHOLD_MB (used in server_cache_storage.go:47)

Server struct fields to remove:
- storageCache, cacheMu, maxCacheSize, cacheTTL, cleanupTicker, cacheHits, cacheMisses

Tests to delete:
- server_eviction_test.go (entire file - 9 tests)
- limits_test.go cache assertions

Special consideration: ValidateDatabase endpoint uses findDatabaseForCwd() outside cache. Verify if used, then remove or inline.

Safe to proceed with removal - cache always had 1 entry in local daemon model.


Fix TestTwoCloneCollision timeout