Drop-in ROM: first-run sidecar conversion, no Python (issue #6) (#84)

* Drop-in ROM: first-run sidecar conversion, no Python (issue #6, Part A + interim)

The release bundle now turns a dropped-in NTSC-U ROM into a playable game
with zero tooling: when data/pcmodels-* / data/pccg-* are missing at boot,
the engine spawns the frozen prepare-assets converter shipped in the bundle
(prepare-assets/ge007-convert[.exe], PyInstaller --onefile), waits for it,
and re-checks before continuing (port/src/romconvert.c, called from
romdataInit after ROM validation). Failure aborts boot with a message
instead of the later D179-class crash.

- prepare-assets.py: runs in-process via runpy when frozen (no user Python
  to exec); NTSC-U-only gate with a clear message for PAL/JP ROMs; d88's
  sibling import needs an explicit sys.path entry (run_path does not set
  one). Verified: frozen exe output byte-identical to the unfrozen path and
  to the shipped sidecars.
- CI (linux + windows): PyInstaller freeze step before bundling
  (ensurepip / --break-system-packages for MSYS2's pip-less python).
- bundle scripts: copy ge007-convert into prepare-assets/ (hard-fail if not
  frozen), size guard 60 -> 120 MB.
- Release notes: US-only drop-in instructions, no Python required.
- D258: PAL/JP filelist naming defects documented; multi-region deferred to
  the Part B follow-up.

* CI: install pip via pacman on Windows (MSYS2 ensurepip is disabled); regen findings index for D258

.github/workflows/ci.yml

@@ -181,7 +181,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y build-essential gcc-14 g++-14 cmake python3 \
-            libsdl2-dev zlib1g-dev libgl1-mesa-dev ccache patchelf
+            python3-pip libsdl2-dev zlib1g-dev libgl1-mesa-dev ccache patchelf
 
       - name: Restore ccache
         uses: actions/cache@v4
@@ -195,6 +195,22 @@ jobs:
       - name: Regenerate ROM-asset symbol file (US)
         run: python3 scripts/gen_romassets.py u
 
+      # Drop-in ROM support: freeze the asset-prep tool into a single
+      # ge007-convert binary the engine spawns on first run when the
+      # pcmodels/pccg sidecars are missing (port/src/romconvert.c). Pure-
+      # stdlib scripts, so PyInstaller --onefile is clean; lands in
+      # tools_pc/dist/prepare-assets/ where bundle-linux.sh picks it up.
+      - name: Freeze asset converter (PyInstaller)
+        run: |
+          python3 -c "import PyInstaller" 2>/dev/null \
+            || python3 -m pip install --quiet --break-system-packages pyinstaller
+          python3 -m PyInstaller --onefile --noconfirm --clean \
+            --name ge007-convert \
+            --distpath tools_pc/dist/prepare-assets \
+            --workpath build-pyinst --specpath build-pyinst \
+            tools_pc/dist/prepare-assets/prepare-assets.py
+          ls -la tools_pc/dist/prepare-assets/ge007-convert
+
       - name: Configure (ntsc-final)
         run: cmake -S . -B build-linux -DROMID=ntsc-final
              -DCMAKE_C_COMPILER=gcc-14 -DCMAKE_CXX_COMPILER=g++-14
@@ -297,6 +313,25 @@ jobs:
       - name: Regenerate ROM-asset symbol file (US)
         run: python scripts/gen_romassets.py u
 
+      # Drop-in ROM support: freeze the asset-prep tool into a single
+      # ge007-convert.exe the engine spawns on first run when the pcmodels/
+      # pccg sidecars are missing (port/src/romconvert.c). Lands in
+      # tools_pc/dist/prepare-assets/ where bundle-win.sh picks it up.
+      - name: Freeze asset converter (PyInstaller)
+        run: |
+          # MSYS2's mingw python ships without pip and has ensurepip
+          # disabled — install pip from pacman, then PyInstaller.
+          python -c "import PyInstaller" 2>/dev/null || {
+            pacman -S --noconfirm mingw-w64-x86_64-python-pip
+            python -m pip install --quiet --break-system-packages pyinstaller
+          }
+          python -m PyInstaller --onefile --noconfirm --clean \
+            --name ge007-convert \
+            --distpath tools_pc/dist/prepare-assets \
+            --workpath build-pyinst --specpath build-pyinst \
+            tools_pc/dist/prepare-assets/prepare-assets.py
+          ls -la tools_pc/dist/prepare-assets/ge007-convert.exe
+
       - name: Build (ntsc-final)
         run: ./build-pc.sh ntsc-final