feat(settings): show the active local data paths

[afurm]

Draftmora is local-first, so users should be able to see where their local board data is stored without reading source code or guessing from the current working directory.

Suggested scope:

• Add a read-only "Local data" area in Settings.
• Show the resolved SQLite board database path from BOARD_DB_PATH or the default ./data/board.db resolution.
• Optionally show the memory file names used by the current workspace: USER.md and MEMORY.md.
• Do not expose API keys, OAuth tokens, provider secrets, or raw memory contents.

Acceptance criteria:

• Settings clearly shows the active board database path.
• Tests cover the server-side value and the Settings UI rendering.
• Existing settings save behavior remains unchanged.
• npm run typecheck and npm test pass.