Improve staleness check error handling and optimization (bd-n4td, bd-o4qy, bd-c4rq)

This commit implements three related improvements to database staleness checking:

**bd-n4td (P2): Add warning when staleness check errors**
- Added stderr warnings when CheckStaleness fails in ensureDatabaseFresh
- Users now see "Warning: could not check database staleness: <error>"
- Provides visibility into staleness check failures while allowing operations to proceed

**bd-o4qy (P2): Improve CheckStaleness error handling**
- Updated CheckStaleness to distinguish between expected and abnormal conditions:
  * Returns (false, nil) for expected "no data yet" scenarios (missing metadata, missing JSONL)
  * Returns (false, err) for abnormal errors (glob failures, permission errors)
- Updated RPC server (2 locations) to log staleness errors but allow requests to proceed
- Prevents blocking operations due to transient staleness check issues
- Added comprehensive function documentation

**bd-c4rq (P3): Refactor staleness check to avoid function call overhead**
- Moved daemon check from inside ensureDatabaseFresh to all 8 call sites
- Avoids unnecessary function call when running in daemon mode
- Updated: list.go, info.go, status.go, show.go, stale.go, duplicates.go, ready.go, validate.go
- Extracted staleness functions to new staleness.go for better organization

**Code review fixes:**
- Removed dead code in CheckStaleness (unreachable jsonlPath == "" check)
- Removed unused ensureDatabaseFreshQuiet function

**Files changed:**
- New: cmd/bd/staleness.go (extracted staleness checking functions)
- Modified: 8 command files (added daemon check before staleness calls)
- Modified: internal/autoimport/autoimport.go (improved error handling)
- Modified: internal/rpc/server_export_import_auto.go (handle errors gracefully)

internal/autoimport/autoimport.go

@@ -250,36 +250,49 @@ func parseJSONL(jsonlData []byte, _ Notifier) ([]*types.Issue, error) {
 
 // CheckStaleness checks if JSONL is newer than last import
 // dbPath is the full path to the database file
+//
+// Returns:
+//   - (true, nil) if JSONL is newer than last import (database is stale)
+//   - (false, nil) if database is fresh or no JSONL exists yet
+//   - (false, err) if an abnormal error occurred (file system issues, permissions, etc.)
 func CheckStaleness(ctx context.Context, store storage.Storage, dbPath string) (bool, error) {
 	lastImportStr, err := store.GetMetadata(ctx, "last_import_time")
 	if err != nil {
+		// No metadata yet - expected for first run
 		return false, nil
 	}
-	
+
 	lastImportTime, err := time.Parse(time.RFC3339, lastImportStr)
 	if err != nil {
+		// Corrupted metadata - not critical, assume not stale
 		return false, nil
 	}
-	
+
 	// Find JSONL using database directory
 	dbDir := filepath.Dir(dbPath)
 	pattern := filepath.Join(dbDir, "*.jsonl")
 	matches, err := filepath.Glob(pattern)
+	if err != nil {
+		// Glob failed - this is abnormal
+		return false, fmt.Errorf("failed to find JSONL file: %w", err)
+	}
+
 	var jsonlPath string
-	if err == nil && len(matches) > 0 {
+	if len(matches) > 0 {
 		jsonlPath = matches[0]
 	} else {
 		jsonlPath = filepath.Join(dbDir, "issues.jsonl")
 	}
-	
-	if jsonlPath == "" {
-		return false, nil
-	}
-	
+
 	stat, err := os.Stat(jsonlPath)
 	if err != nil {
-		return false, nil
+		if os.IsNotExist(err) {
+			// JSONL doesn't exist - expected for new repo
+			return false, nil
+		}
+		// Other stat error (permissions, etc.) - abnormal
+		return false, fmt.Errorf("failed to stat JSONL file %s: %w", jsonlPath, err)
 	}
-	
+
 	return stat.ModTime().After(lastImportTime), nil
 }

internal/rpc/server_export_import_auto.go

@@ -184,8 +184,13 @@ func (s *Server) checkAndAutoImportIfStale(req *Request) error {
 	// Fast path: Check if JSONL is stale using cheap mtime check
 	// This avoids reading/hashing JSONL on every request
 	isStale, err := autoimport.CheckStaleness(ctx, store, dbPath)
-	if err != nil || !isStale {
-		return err
+	if err != nil {
+		// Log error but allow request to proceed (don't block on staleness check failure)
+		fmt.Fprintf(os.Stderr, "Warning: failed to check staleness: %v\n", err)
+		return nil
+	}
+	if !isStale {
+		return nil
 	}
 
 	// Single-flight guard: Only allow one import at a time
@@ -220,8 +225,13 @@ func (s *Server) checkAndAutoImportIfStale(req *Request) error {
 
 	// Double-check staleness after acquiring lock (another goroutine may have imported)
 	isStale, err = autoimport.CheckStaleness(ctx, store, dbPath)
-	if err != nil || !isStale {
-		return err
+	if err != nil {
+		// Log error but allow request to proceed (don't block on staleness check failure)
+		fmt.Fprintf(os.Stderr, "Warning: failed to check staleness: %v\n", err)
+		return nil
+	}
+	if !isStale {
+		return nil
 	}
 
 	// Create timeout context for import operation (bd-8931, bd-1048)