Add database fingerprinting and validation (bd-166)

- Add fingerprint.go with robust URL canonicalization
  - Handles git@, ssh://, https://, http://, file://, and local paths
  - Normalizes URLs to produce consistent repo_id across formats
  - Clone ID uses git repo root for stability

- Update init.go to store repo_id and clone_id metadata
  - repo_id: SHA256 hash of canonical git remote URL
  - clone_id: SHA256 hash of hostname + repo root path

- Add daemon validation to prevent database mismatches
  - Validates repo_id on daemon start
  - Fails on legacy databases (requires explicit migration)
  - Clear error messages with actionable solutions

- Add migrate --update-repo-id command
  - Updates repo_id after remote URL changes
  - Confirmation prompt (can bypass with --yes)
  - Supports --dry-run

Prevents accidental database mixing across repos and provides
migration path for remote URL changes or bd upgrades.

Closes bd-166

Amp-Thread-ID: https://ampcode.com/threads/T-a9d9dab1-5808-4f62-93ea-75a16cca978b
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/init.go

@@ -131,9 +131,9 @@ bd.db
 		// Set the issue prefix in config
 		ctx := context.Background()
 		if err := store.SetConfig(ctx, "issue_prefix", prefix); err != nil {
-			fmt.Fprintf(os.Stderr, "Error: failed to set issue prefix: %v\n", err)
-			_ = store.Close()
-			os.Exit(1)
+		fmt.Fprintf(os.Stderr, "Error: failed to set issue prefix: %v\n", err)
+		_ = store.Close()
+		os.Exit(1)
 		}
 
 		// Store the bd version in metadata (for version mismatch detection)
@@ -142,6 +142,34 @@ bd.db
 		// Non-fatal - continue anyway
 		}
 
+	// Compute and store repository fingerprint
+	repoID, err := beads.ComputeRepoID()
+	if err != nil {
+		if !quiet {
+			fmt.Fprintf(os.Stderr, "Warning: could not compute repository ID: %v\n", err)
+		}
+	} else {
+		if err := store.SetMetadata(ctx, "repo_id", repoID); err != nil {
+			fmt.Fprintf(os.Stderr, "Warning: failed to set repo_id: %v\n", err)
+		} else if !quiet {
+			fmt.Printf("  Repository ID: %s\n", repoID[:8])
+		}
+	}
+
+	// Store clone-specific ID
+	cloneID, err := beads.GetCloneID()
+	if err != nil {
+		if !quiet {
+			fmt.Fprintf(os.Stderr, "Warning: could not compute clone ID: %v\n", err)
+		}
+	} else {
+		if err := store.SetMetadata(ctx, "clone_id", cloneID); err != nil {
+			fmt.Fprintf(os.Stderr, "Warning: failed to set clone_id: %v\n", err)
+		} else if !quiet {
+			fmt.Printf("  Clone ID: %s\n", cloneID)
+		}
+	}
+
 		// Create config.json for explicit configuration
 		if useLocalBeads {
 			cfg := configfile.DefaultConfig(Version)