🦀 Native Workshop browser, catalog backend and three build variants

[PyXiion]

Greetings, PyXiion! The silicon-based contributor is here.

What this adds

Native QML Workshop browser (src/pxmodrim/ui/plugins/workshop/, src/pxmodrim/core/workshop/)

• Discover, Mods, Collections and Installed tabs, catalog filters (game version, searchable known-tag picker, sort), detail pages with the same description renderer as Mod Info.
• Dependency-aware downloads into Local mods that never subscribe or activate; background queue with progress in the header; stale-while-revalidate page cache (memory + disk).
• Installed cards and detail pages get Activate/Deactivate; fully downloaded collections get Activate all / Deactivate all / Activate only this pack (same UX as the Steam web integration); colour-coded buttons; vote percentages, size and score on cards.
• Listing grids are virtualised and hidden grids freed; the Installed list is reused for 5 minutes (memory stays flat while switching tabs: 308 -> 194 MB over three rounds on 2047 mods).

Catalog backend (cf-workers/, TypeScript Cloudflare Worker)

• Public read-only catalog API over Steam with D1 stores, FTS5 search index, crawler, query-page cache and stale-while-revalidate. Production Wrangler config stays out of the repo; all migrations through 0007_collection_compatibility.sql must be applied before deploying.

Build variants (packaging/build.py, .github/workflows/build.yml)

• NoWorkshop (no downloader, no Downloads tab, no browser, PxSteamDL not built), SteamWorkshop (downloader + web browser), NativeWorkshop (downloader + native browser, no WebEngine); CI builds all three on Linux, macOS and Windows and names artifacts by variant.
• build.yml runs on v* tags and manual dispatch. The published branch previously completed the full build matrix; v0.3.0 will rebuild every variant from the merged release commit.

Verification

• Final local just ci: ruff, formatting, pyright (0 errors), layer check, 763 tests pass; backend TypeScript check, bundled Worker dry run and 40 tests pass.
• Real-display smoke runs of Discover, Mods, detail, collection pages, Back and shutdown on Wayland; memory measured with memray.
• Final offscreen application startup loaded 2091 mods, initialized the native Workshop plugins and reported running version 0.3.0.
• Not run locally: full Nuitka builds of the three variants.
• Final release-focused review found no evidence-backed blocking correctness/security bugs.
• Release metadata prepared for v0.3.0. Codacy binary-artwork exclusions address its observed SARIF UTF-8 formatter crash; source scanning remains enabled.