M10.8: desktop CI lane (.forgejo/workflows/desktop.yml) + app-icon source

Separate workflow (not ci.yml) so the ~20-40min Rust/AppImage build only runs on
desktop/** changes, not every backend/frontend push. Builds on the ci-tauri:1.97
image: frontend build -> `cargo tauri icon app-icon.png` (from a committed 1024px
source PNG, sidestepping SVG-input questions) -> cargo fmt --check -> clippy -D
warnings -> cargo test -> `cargo tauri build` (deb + AppImage).
APPIMAGE_EXTRACT_AND_RUN=1 for FUSE-less CI containers. Verifies the M10.2 scaffold
end-to-end and is the foundation for the integrated-AppImage work (task 2013).
Also updates ci-requirements.md with the desktop lane.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

ci-requirements.md

@@ -45,3 +45,22 @@ entirely on `ci-python:3.14`.
   (family rule 46).
 - The production runtime `Dockerfile` tracks python:3.12 so test results stay
   representative of the deployed image.
+
+## Desktop (Tauri) lane — separate workflow
+
+The Tauri desktop client (`desktop/`) builds in its own workflow,
+`.forgejo/workflows/desktop.yml`, NOT in `ci.yml` — it's a heavy Rust + AppImage
+build (~20–40 min) that should only run on `desktop/**` changes, not on every
+backend/frontend push.
+
+- **Image:** `git.fabledsword.com/bvandeusen/ci-tauri:1.97` (Rust + Node +
+  WebKitGTK 4.1 + Tauri v2 Linux deps + `tauri-cli`). Selected via
+  `container.image`; `runs-on: python-ci` is only a scheduling label.
+- **Steps:** build the shared frontend (embedded by `generate_context!`) →
+  `cargo tauri icon app-icon.png` (platform icon set from the committed 1024px
+  source) → `cargo fmt --check` → `cargo clippy -D warnings` → `cargo test` →
+  `cargo tauri build` (produces `.deb` + `.AppImage`).
+- **`APPIMAGE_EXTRACT_AND_RUN=1`** is set: AppImage tooling FUSE-mounts by default
+  and CI containers have no `/dev/fuse`.
+- No Postgres lane (unchanged): the desktop app's local store + sync behavior is
+  verified on the operator's machine, not in CI.