Install the MCP server with QElectroTech

The MCP server (misc/qet-mcp) was only reachable from a source checkout.
It now ships with every package, next to the program, and finds that
QElectroTech and its element collection from where it sits:

- make install (Linux distributions, snap, flatpak):
  <prefix>/share/qelectrotech/mcp/qet_mcp.py, executable, with its README.
- Windows installer: a new "AI assistant (MCP)" component (on by default,
  ~200 KB), installed to <folder>\mcp. The workflow stages files/mcp, so
  the portable folder and the MSI, which packs all of files/, carry it too.

The server learns the Windows layout (<root>/mcp beside <root>/bin, whose
program is QElectroTech.exe, and <root>/elements), in addition to
<prefix>/share/qelectrotech/mcp. A copy saved anywhere else, even beside
some bin/ folder, is not taken for an installation.

The installer strings are given in all 29 installer languages: French
translated, the others in English until translated, which is what NSIS
would fall back to anyway but without its warning 6040 per language.

Checked: make install into a scratch prefix, then from the installed
script with nothing configured and no qelectrotech on PATH, an SVG export
and a qet_edit placing a common:// element both succeeded. makensis 3.10
compiles the installer with 0 warnings before and after (removing the
French description gives warning 6040), and the installer contains
mcp/qet_mcp.py. Suite 274/274 none skipped; each layout check was
removed in turn and a test failed. Snap/flatpak: installed by the same
CMake rule; launching their QElectroTech from outside is untested.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/windows-build.yml

@@ -227,6 +227,9 @@ jobs:
           cp -r "$GITHUB_WORKSPACE/titleblocks" "$FILES/titleblocks" || true
           cp -r "$GITHUB_WORKSPACE/examples"    "$FILES/examples"    || true
           cp -r "$GITHUB_WORKSPACE/fonts"       "$FILES/fonts"       || true
+          # The MCP server finds bin/QElectroTech.exe and elements/ from mcp/.
+          mkdir -p "$FILES/mcp"
+          cp "$GITHUB_WORKSPACE/misc/qet-mcp/qet_mcp.py" "$GITHUB_WORKSPACE/misc/qet-mcp/README.md" "$FILES/mcp/"
 
           # --- Translations ---
           # Since PR #751 the .qm files are no longer tracked in git: lrelease
@@ -305,7 +308,7 @@ jobs:
               && echo "  OK      : $f" \
               || echo "  MISSING: $f"
           done
-          for d in ico elements lang titleblocks fonts examples bin; do
+          for d in ico elements lang titleblocks fonts examples bin mcp; do
             [ -d "$FILES/$d" ] \
               && echo "  OK      : $d/" \
               || echo "  MISSING: $d/"