Add a daemon setting `autoArchiveAfterMerge` (default off). When on, the
daemon's existing GitHub poll triggers archive once the PR is merged,
but only if the worktree is clean (not dirty, not ahead of origin).
Skips silently otherwise.
Adds a per-provider toggle in Settings → Providers, persisted via daemon
config, so users can turn off providers they don't have installed (or
don't want to use) without removing them from the registry.
Disabled providers stay visible everywhere — settings, `paseo provider
ls`, MCP `list_providers`, model/mode lists — marked as disabled rather
than silently filtered. Availability probes are skipped for them, and
attempts to launch an agent or fetch models/modes from a disabled
provider return a clear "Provider '<id>' is disabled" error.
Schema additions (`enabled` on `ProviderSnapshotEntry`, MCP provider
summary) are backward-compatible: optional with a default of true so
older clients continue to parse new daemon messages.
CLI: `paseo provider ls` gains an ENABLED column; JSON output includes
the new field.
