Add exclude patterns, snapshot prune, and other improvements

- Implement exclude patterns with anchored pattern support:
  - Patterns starting with / only match from root of source dir
  - Unanchored patterns match anywhere in path
  - Support for glob patterns (*.log, .*, **/*.pack)
  - Directory patterns skip entire subtrees
  - Add gobwas/glob dependency for pattern matching
  - Add 16 comprehensive tests for exclude functionality

- Add snapshot prune command to clean orphaned data:
  - Removes incomplete snapshots from database
  - Cleans orphaned files, chunks, and blobs
  - Runs automatically at backup start for consistency

- Add snapshot remove command for deleting snapshots

- Add VAULTIK_AGE_SECRET_KEY environment variable support

- Fix duplicate fx module provider in restore command

- Change snapshot ID format to hostname_YYYY-MM-DDTHH:MM:SSZ

internal/database/database.go

@@ -205,6 +205,15 @@ func NewTestDB() (*DB, error) {
 	return New(context.Background(), ":memory:")
 }
 
+// repeatPlaceholder generates a string of ", ?" repeated n times for IN clause construction.
+// For example, repeatPlaceholder(2) returns ", ?, ?".
+func repeatPlaceholder(n int) string {
+	if n <= 0 {
+		return ""
+	}
+	return strings.Repeat(", ?", n)
+}
+
 // LogSQL logs SQL queries and their arguments when debug mode is enabled.
 // Debug mode is activated by setting the GODEBUG environment variable to include "vaultik".
 // This is useful for troubleshooting database operations and understanding query patterns.