Fix all test failures from bd-166 (missing issue_prefix)

Completed bd-167: Fixed all tests that failed with 'database not initialized: issue_prefix config is missing' error.

Changes:
- Created test helper functions in 3 locations:
  * cmd/bd/test_helpers_test.go (already existed)
  * internal/rpc/test_helpers.go (new)
  * internal/storage/sqlite/test_helpers.go (new)

- Updated all affected test files to use newTestStore():
  * cmd/bd: comments, export, git_sync, label, list, reopen, direct_mode
  * internal/rpc: rpc_test, version_test
  * internal/storage/sqlite: sqlite_test, underlying_db_test

- Fixed config test: updated flush-debounce default from 5s to 30s

- Removed unused sqlite imports from test files

All tests now passing ✅

Also:
- Closed bd-167, bd-170 (cleanup of beads-* duplicates)
- Removed corrupt backup files

Amp-Thread-ID: https://ampcode.com/threads/T-4a8c6002-9384-45b6-81f6-2907d1e4c6c2
Co-authored-by: Amp <amp@ampcode.com>

internal/rpc/rpc_test.go

@@ -435,10 +435,7 @@ func TestDatabaseHandshake(t *testing.T) {
 	os.MkdirAll(beadsDir1, 0750)
 	dbPath1 := filepath.Join(beadsDir1, "db1.db")
 	socketPath1 := filepath.Join(beadsDir1, "bd.sock")
-	store1, err := sqlitestorage.New(dbPath1)
-	if err != nil {
-		t.Fatalf("Failed to create store 1: %v", err)
-	}
+	store1 := newTestStore(t, dbPath1)
 	defer store1.Close()
 
 	server1 := NewServer(socketPath1, store1, tmpDir1, dbPath1)
@@ -453,10 +450,7 @@ func TestDatabaseHandshake(t *testing.T) {
 	os.MkdirAll(beadsDir2, 0750)
 	dbPath2 := filepath.Join(beadsDir2, "db2.db")
 	socketPath2 := filepath.Join(beadsDir2, "bd.sock")
-	store2, err := sqlitestorage.New(dbPath2)
-	if err != nil {
-		t.Fatalf("Failed to create store 2: %v", err)
-	}
+	store2 := newTestStore(t, dbPath2)
 	defer store2.Close()
 
 	server2 := NewServer(socketPath2, store2, tmpDir2, dbPath2)