refactor(database, connections): dedup post-connect setup, extract StoredConnection model

[datlechin]

Summary

Two behavior-preserving Tier-1 architecture refactors. Both build green; the connect/reconnect change was manually verified in the running app (connect + reconnect + startup commands), and the model extraction is covered by the existing ConnectionStorage Codable tests.

1. Shared post-connect setup (DatabaseManager)

The post-connect sequence (apply query timeout, run startup commands; restore schema/database on reconnect) was duplicated across reconnectDriver, reconnectSession, and connectToSession. Extracted into two helpers, applyTimeoutAndStartupCommands and restoreSchemaAndDatabase.

Each call site keeps its own distinct pre-connect orchestration (tunnel rebuild, password prompt, connect error handling) and passes its exact original arguments (for example connectToSession keeps resolvedConnection.startupCommands and connection.name), so behavior is unchanged. Net +42 / -52.

2. Extract StoredConnection model

ConnectionStorage.swift was a 988-line file mixing connection CRUD, 8 kinds of Keychain secret storage, migrations, and the 420-line StoredConnection Codable model. Moved StoredConnection to its own file. ConnectionStorage.swift is now 565 lines, under all SwiftLint limits. Pure move, no logic change.

Verification

• App build: green.
• Connect + reconnect + startup-commands flow: manually verified in the running app.
• Connection list load + save: manually verified; the ConnectionStorage Codable round-trip is covered by existing tests in CI.

Notes

This is the safe, verifiable slice of Tier 1. The remaining items (split the 8 Keychain secret methods into a ConnectionSecretsStore, the DI singleton sweep, and the MainContentCoordinator god-object split) are higher-risk and were deliberately deferred to dedicated work where the running app can be driven to verify password, connection, and UI behavior.