feat(linux): add Flatpak CI, .deb builder, and AUR PKGBUILD

[cozyGarage]

Summary

• Add `.github/workflows/flatpak-linux.yml` to build `linux/flatpak/com.tablepro.linux.json` with `flatpak-builder` on GNOME 47.
• Vendor GtkSourceView 5.16 into the Flatpak manifest; keep `scripts/build-flatpak.sh` and `scripts/generate-cargo-sources.sh` for local / Flathub offline flows.
• Add Debian packaging under `linux/packaging/debian/` plus `scripts/build-deb.sh` (produces a rootless `.deb`).
• Add an AUR `PKGBUILD` and packaging README. Update AppStream metainfo for MSSQL / ClickHouse.

Test plan

• `python3 -c 'import json; json.load(open("flatpak/com.tablepro.linux.json"))'`
• `./scripts/build-deb.sh` → `packaging/out/tablepro_0.1.0-1_amd64.deb` (6.5 MB) with expected Depends
• GtkSourceView tarball sha256 verified against gnome.org
• CI Flatpak job green on this PR
• Optional local: `./scripts/build-flatpak.sh` after installing flatpak runtimes

Made with Cursor

[cozyGarage]

I have read the CLA Document and I hereby sign the CLA.

[datlechin]

Hi @cozyGarage, could you please resolve the conflict with linux branch?

[cozyGarage]

Rebased onto latest linux and resolved the conflicts.

• Dropped the stacked ClickHouse commit (tracked in feat(drivers): add ClickHouse driver via official clickhouse crate #1979)
• Skipped the obsolete .local-deps / dev-env.sh commit (already on linux)
• Aligned Flatpak metainfo with drivers currently registered on linux (no ClickHouse yet)

[cozyGarage]

Flatpak CI failed on an obsolete Meson flag: gtksourceview 5.16 renamed -Dgtk_doc to -Ddocumentation. Pushed a one-line fix.

[cozyGarage]

Flatpak still failed after the Meson flag fix: GtkSourceView 5.16 needs GTK ≥ 4.17, but the GNOME 47 runtime only has 4.16.13.

Pinned the module to 5.14.2 (the GNOME 47-era series, GTK ≥ 4.6). CI should get past that module now.

[cozyGarage]

Next failure was expected offline Flatpak sandboxing: Cargo could not resolve index.crates.io.

Gave the tablepro-app module build-args: [--share=network] so CI can fetch crates. That is fine for this workflow; Flathub still needs generated-sources.json (script already documented in linux/packaging/README.md).