Major refactoring: UUID-based storage, streaming architecture, and CLI improvements

This commit represents a significant architectural overhaul of vaultik:

Database Schema Changes:
- Switch files table to use UUID primary keys instead of path-based keys
- Add UUID primary keys to blobs table for immediate chunk association
- Update all foreign key relationships to use UUIDs
- Add comprehensive schema documentation in DATAMODEL.md
- Add SQLite busy timeout handling for concurrent operations

Streaming and Performance Improvements:
- Implement true streaming blob packing without intermediate storage
- Add streaming chunk processing to reduce memory usage
- Improve progress reporting with real-time metrics
- Add upload metrics tracking in new uploads table

CLI Refactoring:
- Restructure CLI to use subcommands: snapshot create/list/purge/verify
- Add store info command for S3 configuration display
- Add custom duration parser supporting days/weeks/months/years
- Remove old backup.go in favor of enhanced snapshot.go
- Add --cron flag for silent operation

Configuration Changes:
- Remove unused index_prefix configuration option
- Add support for snapshot pruning retention policies
- Improve configuration validation and error messages

Testing Improvements:
- Add comprehensive repository tests with edge cases
- Add cascade delete debugging tests
- Fix concurrent operation tests to use SQLite busy timeout
- Remove tolerance for SQLITE_BUSY errors in tests

Documentation:
- Add MIT LICENSE file
- Update README with new command structure
- Add comprehensive DATAMODEL.md explaining database schema
- Update DESIGN.md with UUID-based architecture

Other Changes:
- Add test-config.yml for testing
- Update Makefile with better test output formatting
- Fix various race conditions in concurrent operations
- Improve error handling throughout

internal/database/database_test.go

@@ -67,21 +67,26 @@ func TestDatabaseConcurrentAccess(t *testing.T) {
 	}()
 
 	// Test concurrent writes
-	done := make(chan bool, 10)
+	type result struct {
+		index int
+		err   error
+	}
+	results := make(chan result, 10)
+
 	for i := 0; i < 10; i++ {
 		go func(i int) {
-			_, err := db.ExecWithLock(ctx, "INSERT INTO chunks (chunk_hash, sha256, size) VALUES (?, ?, ?)",
+			_, err := db.ExecWithLog(ctx, "INSERT INTO chunks (chunk_hash, sha256, size) VALUES (?, ?, ?)",
 				fmt.Sprintf("hash%d", i), fmt.Sprintf("sha%d", i), i*1024)
-			if err != nil {
-				t.Errorf("concurrent insert failed: %v", err)
-			}
-			done <- true
+			results <- result{index: i, err: err}
 		}(i)
 	}
 
-	// Wait for all goroutines
+	// Wait for all goroutines and check results
 	for i := 0; i < 10; i++ {
-		<-done
+		r := <-results
+		if r.err != nil {
+			t.Fatalf("concurrent insert %d failed: %v", r.index, r.err)
+		}
 	}
 
 	// Verify all inserts succeeded