chore: remove cloud sync code and daemon sync timer

[franzer]

Removes the hosted-cloud sync path now that git-ref sync (per-repo lore sync and global lore sync --global) is shipped. Local capture and git-ref sync are untouched.

• Deletes the cloud client, the lore login/logout/cloud commands, and the cloud module (encryption already lives in sync/).
• Drops the daemon's 4-hour sync timer; the daemon reverts to capture, auto-link, and auto-summarize. File watcher and IPC server unchanged.
• Removes the cloud_url config; keeps encryption_salt, machine_id, use_keychain, sync_global_remote, and the summary config.
• Prunes now-unused deps (webbrowser, base64); keeps reqwest (summary providers), keyring (keystore), and the sync crypto deps.

Net: +51 / -4184 (about -4.1k lines). The hosted service (Vercel/Turso) stays up for now and will be turned off separately; a lore-www "cloud retired" note lands with 29.7.

Note: two Database methods (get_unsynced_sessions, import_session_with_messages) lost their production caller but are retained as widely-used test fixtures under #[allow(dead_code)] (matching existing convention for tested-but-unexported helpers).

Tests: full suite green (1,203), clippy -D warnings clean; lore sync/--global, capture, daemon file-watch/auto-link/auto-summarize all still pass.