feat(m9): .deb package + CI build/publish — 0.35.0

packaging/make_deb.py builds rigdoctor_<ver>_all.deb (Architecture: all) via
dpkg-deb, no debhelper: Depends python3; Recommends python3-pyside6/pyte (GUI by
default, --no-install-recommends = CLI only). Installs the package, both
launchers, desktop entry + icon; postinst refreshes the desktop database.
release.yml builds it as a release asset and optionally pushes to the Gitea apt
registry (REGISTRY_TOKEN). Verified locally: valid .deb, packaged launcher runs
'rigdoctor --version'. Docs/README/ROADMAP/MODULES updated; M9 complete.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -78,6 +78,26 @@ also ships a one-file **`.run`** installer (download, `chmod +x`, run). Updates
 accounts on the Git server (a Personal Access Token); save one via the GUI **Setup → Update
 access** panel or `rigdoctor login`, then `rigdoctor update` (or the sidebar button).
 
+## Install (`.deb`, system-wide)
+
+Each release also ships a **`.deb`** (`Architecture: all`, M9/D8). Download it from the release
+and install with apt (pulls the GUI deps — PySide6/pyte — via Recommends):
+
+```bash
+sudo apt install ./rigdoctor_<version>_all.deb     # CLI-only: add --no-install-recommends
+```
+
+When the apt registry is enabled on the server, you can instead add it as a source and
+`sudo apt update && sudo apt install rigdoctor` (with `apt upgrade` for updates):
+
+```bash
+curl -fsSL https://git.jesseyvanofferen.com/api/packages/jessey/debian/repository.key \
+  | sudo tee /etc/apt/keyrings/gitea-rigdoctor.asc > /dev/null
+echo "deb [signed-by=/etc/apt/keyrings/gitea-rigdoctor.asc] \
+  https://git.jesseyvanofferen.com/api/packages/jessey/debian stable main" \
+  | sudo tee /etc/apt/sources.list.d/rigdoctor.list
+```
+
 ## Run it (dev)
 
 Stdlib-only, no install needed (target is Python ≥ 3.11; tested on 3.14):