[hmziqagent]

Adds Snap as a backend in toride-apps, end to end except registry routing.

Planner. Operation::SnapInstall { name, channel }, SnapUninstall, and SnapUpdate render snap install [--channel=<track>/<risk>[/branch]], snap remove, and snap refresh. There is no InstallMethod::Snap yet (snapcraft.io source data is a later registry round), so snap operations are constructed at the operation seam — the argv contract is the same as every routed method's.

SnapBackend (backends/snap.rs) executes them through the shared CommandRunner:

• detect() is a PATH check — no command runs.
• version() reads the snap <version> client row from snap version.
• install/remove/refresh follow snapd's real idempotency: the bare exit-0 "already installed" / "not installed" notices are successes; everything else (error: with exit 1, snapd unreachable, unknown snap) surfaces as Error::Command carrying snapd's stderr.
• list/status/outdated parse snapd's tabwriter tables (two-or-more-space separators, - placeholders). A malformed row is skipped, never fatal to the listing; a non-empty document where nothing parses is treated as unparseable output, not an empty host.

Detection and facade. MultiSourceDetector gains a DetectionSource::Snap probe over the installed listing. AppsBuilder grows a snap slot plus auto-attach, records carry NativeIds::Snap { name } so uninstall and update replay snap remove / snap refresh from the recorded name alone, and status routes snap through the recorded/foreign presence seams, async and sync.

Snap-less hosts. An absent snap binary makes detect() return BinaryNotFound, which the builder skips like any other missing manager — nothing errors, snap installs answer BackendUnavailable, and status never probes the slot.

Tests. Offline suites pin argv, table parsing, and the facade flows (adopt / update / uninstall) against strict FakeRunner fakes with tabwriter-shaped fixtures. tests/live.rs, gated behind TORIDE_APPS_INTEGRATION, exercises detect() and the read-only version / list / per-snap status probes against the real host, branching on whether snap exists — no mutating command anywhere.

Gates: test, fmt, clippy, doc, workspace-check — all pass.