feat(store): plugin store host module — signed catalogs, tiered trust, install jobs

The index is the verification gate: a catalog entry pins one exact version
plus that version's tarball integrity hash, so 'verified on every release'
is a property of the data rather than a promise about process. Nothing can
express 'track latest' for a catalogued plugin.

- store/index.rs   signed index parse + ed25519 verify (ring), validate-and-drop
                   per entry, semver minHost/advisory ranges
- store/sources.rs built-in unom source (compiled-in URL + two key slots for
                   rotation) + operator sources in plugin-sources.json
- store/catalog.rs https fetch with size/timeout/redirect caps, signature before
                   parse, last-good disk cache (stale-but-usable when offline)
- store/jobs.rs    single-flight install/uninstall: registry-integrity preflight
                   against the pin, spawn the runner CLI with live log capture,
                   post-install version check with rollback, provenance record,
                   runner restart (discovery is startup-only)
- store/manifest.rs install provenance; absence means CLI-installed
- mgmt/store.rs    12 routes under /api/v1/store, denied to the plugin token
                   (a plugin that can install plugins is an escalation primitive)

Also generalizes runner discovery and listInstalled from @punktfunk/plugin-*
to ANY scope's plugin-*: catalog entries must be scoped so the scope can map
to that entry's registry, so a third-party plugin necessarily arrives under
its own scope and would otherwise install but never run.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/punktfunk-host/src/main.rs

@@ -74,6 +74,9 @@ mod session_plan;
 mod session_status;
 mod spike;
 mod stats_recorder;
+// The plugin store: signed catalogs, tiered trust, and install/uninstall jobs that run through the
+// same runner CLI the `plugins` subcommand uses (design/plugin-store.md).
+mod store;
 mod stream_marker;
 // `monitor_devnode::startup_recover()` (below) re-enables PnP monitor devnodes disabled by a prior
 // run; it lives in the `pf-win-display` leaf crate (plan §W6).