web_interface: fix run.bat fallback + UTF-8 console handling

run.bat:
- Use enabledelayedexpansion so the python/python3 fallback after a missing py launcher actually runs (the previous %ERRORLEVEL% in the parenthesized else block was expanded at parse time, making the fallback unreachable).
- Set chcp 65001, PYTHONUTF8=1, PYTHONIOENCODING=utf-8 so prints with em-dashes do not crash on cp1252/cp932 consoles.

app.py: reconfigure stdout/stderr with errors=replace at startup so non-UTF-8 consoles cannot crash the launcher with UnicodeEncodeError.

web_interface/app.py

@@ -645,6 +645,15 @@ def _run_app() -> None:
 # ---------------------------------------------------------------------------
 
 def main() -> None:
+    # On Windows, the console codepage is often cp1252/cp932/etc., not UTF-8.
+    # Our messages contain em-dashes and × — `errors="replace"` keeps them from
+    # crashing the bootstrap with UnicodeEncodeError on those consoles.
+    for stream in (sys.stdout, sys.stderr):
+        try:
+            stream.reconfigure(errors="replace")
+        except (AttributeError, OSError):
+            pass
+
     force = "--reinstall" in sys.argv[1:]
     if not _in_target_venv():
         _bootstrap(force_reinstall=force)

web_interface/run.bat

@@ -1,25 +1,50 @@
 @echo off
-setlocal
+setlocal enabledelayedexpansion
 cd /d "%~dp0"
 
-rem Prefer the per-user py launcher; fall back to python on PATH.
+rem Force a UTF-8 console + UTF-8 mode in Python so prints with em-dashes and
+rem the like don't crash on machines whose console codepage is cp1252 / cp932.
+chcp 65001 >nul 2>nul
+set "PYTHONUTF8=1"
+set "PYTHONIOENCODING=utf-8"
+
+rem Pick a Python launcher. Try py first (works on most python.org installs),
+rem then `python`, then `python3`. enabledelayedexpansion + !ERRORLEVEL! is
+rem required so each check reads the value AFTER the preceding `where` runs.
+set "PYCMD="
+
 where py >nul 2>nul
-if %ERRORLEVEL%==0 (
-    py "%~dp0app.py" %*
-) else (
+if !ERRORLEVEL! EQU 0 set "PYCMD=py"
+
+if not defined PYCMD (
     where python >nul 2>nul
-    if %ERRORLEVEL%==0 (
-        python "%~dp0app.py" %*
-    ) else (
-        echo [run.bat] No Python found. Install Python 3.10+ from python.org or the Microsoft Store.
-        pause
-        exit /b 1
-    )
+    if !ERRORLEVEL! EQU 0 set "PYCMD=python"
+)
+
+if not defined PYCMD (
+    where python3 >nul 2>nul
+    if !ERRORLEVEL! EQU 0 set "PYCMD=python3"
 )
 
-if %ERRORLEVEL% NEQ 0 (
+if not defined PYCMD (
+    echo [run.bat] No Python found on PATH.
+    echo [run.bat] Install Python 3.10+ from https://www.python.org/downloads/
+    echo [run.bat] During install, tick "Add Python to PATH".
+    pause
+    exit /b 1
+)
+
+echo [run.bat] Using !PYCMD! to launch app.py.
+echo [run.bat] First run creates .venv and installs ~500 MB of packages.
+echo [run.bat] That can take several minutes; it only happens once.
+echo.
+
+!PYCMD! "%~dp0app.py" %*
+set "EXITCODE=!ERRORLEVEL!"
+
+if !EXITCODE! NEQ 0 (
     echo.
-    echo [run.bat] app.py exited with code %ERRORLEVEL%.
+    echo [run.bat] app.py exited with code !EXITCODE!.
     pause
 )
-endlocal
+endlocal & exit /b %EXITCODE%