feat(library): Lutris + Heroic store providers (Linux)

LutrisProvider reads the local pga.db (rusqlite, read-only/immutable so a running
Lutris can't block us) → installed games, launch via `lutris lutris:rungameid/<id>`,
cover art from Lutris's on-disk cache inlined as data: URLs (no public CDN keyed by a
stable id, unlike Steam/Heroic). HeroicProvider parses Heroic's store_cache JSON —
legendary/gog/nile = Epic+GOG+Amazon in one provider — installed-only with an
install-dir existence cross-check (works around Heroic's gog is_installed bug #2691),
free public CDN cover art, launch via `heroic --no-gui heroic://launch?...` (the
single-instance-Electron gamescope-escape caveat is documented; needs live confirm).

New command_for arms (lutris_id digits-guard, heroic runner+appName-guard) + both
providers wired into all_games(); everything Linux-gated (the launchers are
Linux-only), so the Windows/macOS host build is unaffected. Deps rusqlite (bundled
SQLite, no system dep) + base64 added to the Linux target only. Unit tests with
sqlite/json fixtures (installed-only filtering, CDN-art mapping, launch guards); live
`library` enumeration returns [] gracefully on a box without the launchers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/Cargo.toml

@@ -85,6 +85,13 @@ wayland-scanner = "0.31"
 wayland-backend = "0.3"
 # Parse `pw-dump` JSON to find gamescope's PipeWire node (gamescope backend).
 serde_json = "1"
+# Read the Lutris library DB (`pga.db`) for the Lutris store provider. `bundled` vendors + compiles
+# SQLite (cc, already needed for ffmpeg/opus) so there's no system libsqlite3 runtime dependency —
+# clean for the deb/rpm/flatpak packaging. Opened read-only/immutable (Lutris may hold it open).
+rusqlite = { version = "0.40", features = ["bundled"] }
+# Inline Lutris's local cover-art JPEGs as `data:` URLs in the library (Lutris has no public CDN
+# keyed by a stable id, unlike Steam/Heroic; a `data:` URL is self-contained — no host-served endpoint).
+base64 = "0.22"
 # Builds/validates the xkb keymap uploaded to the virtual keyboard + tracks modifier state.
 xkbcommon = "0.8"
 # The safe `opus` crate is stereo-only; surround (5.1/7.1) needs the libopus *multistream*