feat(restore): add weighted progress, pre-extraction disk check, parallel-dbs flag

Three high-value improvements for cluster restore:

1. Weighted progress by database size
   - Progress now shows percentage by data volume, not just count
   - Phase 3/3: Databases (2/7) - 45.2% by size
   - Gives more accurate ETA for clusters with varied DB sizes

2. Pre-extraction disk space check
   - Checks workdir has 3x archive size before extraction
   - Prevents partial extraction failures when disk fills mid-way
   - Clear error message with required vs available GB

3. --parallel-dbs flag for concurrent restores
   - dbbackup restore cluster archive.tar.gz --parallel-dbs=4
   - Overrides CLUSTER_PARALLELISM config setting
   - Set to 1 for sequential restore (safest for large objects)

internal/dedup/chunker_test.go

@@ -103,7 +103,7 @@ func TestChunker_ShiftedData(t *testing.T) {
 	// Test that shifted data still shares chunks (the key CDC benefit)
 	// Use deterministic random data for reproducible test results
 	rng := mathrand.New(mathrand.NewSource(42))
-	
+
 	original := make([]byte, 100*1024)
 	rng.Read(original)