feat(ci): re-enable Linux release builds (CPU, deb+rpm)

Linux shipped briefly in March 2026 (b580189..103e98b) then was removed
with the message "github runners suck." The post-mortem: standard
ubuntu-22.04 hit disk-pressure during pip+PyInstaller, and a namespace
custom-runner attempt proved flaky. Nothing in the app itself was the
problem — the NVIDIA-package exclusions in build_binary.py (~3 GB
shaved from CPU builds), the CPU-only torch install order, the
PulseAudio/PipeWire audio capture code, and the Tauri deb/rpm bundle
targets all still work.

This restores ubuntu-22.04 to the release matrix as a CPU-only Linux
build with a disk-space cleanup step (jlumbroso/free-disk-space) to
address the root cause of the March failures. Ships .deb + .rpm only
— AppImage was explicitly dropped in e18757b due to glibc portability
issues, keeping that decision.

CUDA-for-Linux is intentionally deferred to a follow-up PR: the
GpuAcceleration.tsx frontend hard-codes CUDA download as Tauri-only
without a Linux branch, and AMD users already get ROCm acceleration
for free on a stock CPU-torch install (backend/app.py:148-160). The
NVIDIA-on-Linux case is the only remaining gap and is non-blocking
for a v1 Linux ship.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

.github/workflows/release.yml

@@ -26,12 +26,32 @@ jobs:
             args: ""
             python-version: "3.12"
             backend: "pytorch"
+          - platform: "ubuntu-22.04"
+            args: "--target x86_64-unknown-linux-gnu --bundles deb,rpm"
+            python-version: "3.12"
+            backend: "pytorch"
 
     runs-on: ${{ matrix.platform }}
 
     steps:
       - uses: actions/checkout@v4
 
+      # Ubuntu runners ship with ~14 GB free; pip + PyInstaller + torch can
+      # peak well above that during the build. Reclaim ~25 GB by pruning
+      # preinstalled toolchains we don't use. This is what likely tripped
+      # the March 2026 Linux release attempts (see commit 103e98b
+      # "github runners suck") — not a code issue, a disk-pressure one.
+      - name: Free up disk space (ubuntu)
+        if: contains(matrix.platform, 'ubuntu') || contains(matrix.platform, 'namespace')
+        uses: jlumbroso/free-disk-space@main
+        with:
+          tool-cache: false
+          android: true
+          dotnet: true
+          haskell: true
+          large-packages: true
+          swap-storage: true
+
       - name: Install dependencies (ubuntu only)
         if: contains(matrix.platform, 'ubuntu') || contains(matrix.platform, 'namespace')
         run: |