perf(storage): resolve connection secrets lazily and handle Keychain errors gracefully in local_db

[ZhuchkaTriplesix]

Summary

In LocalDb.getConnections (lib/core/storage/local_db.dart, lines 430–454):

final futures = rows.map((m) => _hydrateConnection(ConnectionRow.fromMap(m)));
return Future.wait(futures);

Where _hydrateConnection unconditionally awaits:

final secrets = await ConnectionSecretsStore.readForConnection(row.id!);

1. Unbounded Parallel Keychain Requests: For N saved connections, Querya launches 2*N simultaneous OS secure storage reads (password and connection_string) on application startup. On Linux (D-Bus org.freedesktop.secrets) and macOS (Keychain), this causes lock contention, IPC bottlenecks, and timeouts (org.freedesktop.DBus.Error.NoReply).
2. Missing Error Handling: _hydrateConnection lacks a try/catch block. If the platform secure store is locked or unavailable (e.g. minimal Linux setup without gnome-keyring or canceled prompt), getConnections() throws, failing to populate the entire connections tree in the sidebar.
3. Unnecessary Eager Resolution: The sidebar tree only requires basic connection metadata (name, host, type, folder). Password and connection string secrets are not needed until the user explicitly initiates a database connection.

Repro

1. Add 20+ database connections.
2. Launch Querya on Linux or macOS.
3. Observe high startup latency or D-Bus timeout errors when hydrating connections; if secure storage errors, no connections render in the UI.

Scope

• Do not eagerly fetch passwords and connection strings for all connections in getConnections().
• Add try/catch in _hydrateConnection and secret store readers to log errors gracefully and preserve basic row data rather than aborting connection tree rendering.
• Resolve secrets on-demand when connect() is invoked for a specific connection.

Out of scope

• Changing the underlying SQLite schema.

[ZhuchkaTriplesix]

Resolved by #947 (already merged into dev; not auto-closed since this repo's default branch is main and PRs merge into dev).