fix(windows): UTF-8 console + self-sufficient validation wrapper

Make the suite run cleanly on Windows.

Product code:
- __init__.py: force UTF-8 on stdout/stderr. The Windows console code
  page (cp1252) cannot encode the box-drawing/accented characters the
  runner prints, which crashed the parent capture_stdout thread. Only
  the stream encoders are reconfigured; the locale default used to read
  cp1252 config files is left untouched.
- report_export_junit/html: open the report file with encoding="utf-8"
  (XML/HTML are UTF-8) instead of the platform default, matching the
  txt/json exporters.

Validation:
- run.bat: source mode now sets up its own venv and runs testium from
  src\ directly instead of delegating to the project run.bat (which
  launches the GUI and drops its arguments). Installs the fake_exporter
  entry-point plugin (report_plugin) and the [lsp] extra, and runs the
  same lsp_check.py pre-flight as run.sh.
- jsonrpc/test.tum: launch the echo server via "$(python_bin)" instead
  of "python3" (the Microsoft Store stub on Windows).
- post_execution.py: write the JUnit XML with encoding="utf-8".
- restore items/run/sub_pass.tum and sub_fail.tum, deleted by mistake in
  d97d00c "removed test logs".

test/validation/items/jsonrpc/test.tum

@@ -20,7 +20,7 @@
             console_name: jrpces
             key: $(test)_PASS
             steps:
-                - writeln: python3 {{include_directory}}/jrpc_echo_server.py -c {{include_directory}}/jrpces.ini
+                - writeln: '"$(python_bin)" {{include_directory}}/jrpc_echo_server.py -c {{include_directory}}/jrpces.ini'
                 - read_until: {expected: ready, timeout: 5}
 
         - console:

test/validation/items/run/sub_fail.tum

@@ -0,0 +1,7 @@
+main:
+    name: run sub-test (always fail)
+    steps:
+        - check:
+            name: fail
+            values:
+                - false

test/validation/items/run/sub_pass.tum

@@ -0,0 +1,7 @@
+main:
+    name: run sub-test (always pass)
+    steps:
+        - check:
+            name: pass
+            values:
+                - true

test/validation/post_execution.py

@@ -89,7 +89,7 @@ def exec():
         junit_report = report.replace(".sqlite", f"-{test}.xml")
         print(junit_report)
         _prepare_file_to_save(junit_report)
-        with open(junit_report, "w") as f:
+        with open(junit_report, "w", encoding="utf-8") as f:
             f.write(TestSuite.to_xml_string([ts]))
 
     # cleanup

test/validation/run.bat

@@ -89,6 +89,13 @@ REM Reports are stamped with the mode so successive runs don't clobber each othe
 
 SET "TAIL=-b -d "python_bin=%VENV_PYTHON%" -d "validation_report_file=validation-%MODE%" -- "%SCRIPT_DIR%\main.tum"%EXTRA%"
 
+REM The report-exporter plugin (items\report_plugin) is a pip entry-point
+REM package. It must live in the *testium* environment, so it is installed into
+REM the source/wheel venvs below. A frozen PyInstaller binary cannot see
+REM externally-installed plugins, so report_plugin is expected to be skipped
+REM there (same as Linux pyinstaller mode).
+SET "FAKE_EXPORTER=%SCRIPT_DIR%\fake_exporter"
+
 REM ---------- per-mode launcher ----------------------------------------------
 
 echo -- validation mode: %MODE%
@@ -100,8 +107,25 @@ echo ERROR: unknown --mode '%MODE%'. Expected: source ^| wheel ^| pyinstaller.
 exit /b 1
 
 :MODE_SOURCE
-call "%PROJECT_DIR%\run.bat" %TAIL%
-exit /b %ERRORLEVEL%
+REM Run testium from src\ in a dedicated venv set up here. We do NOT delegate to
+REM the project's run.bat: that one launches the GUI and does not forward its
+REM arguments, so the suite would never run head-less.
+SET "TESTIUM_VENV=%PROJECT_DIR%\test\tmp\testium_venv"
+IF NOT EXIST "%TESTIUM_VENV%" (
+    echo Creating testium venv at %TESTIUM_VENV%
+    %PYTHON_EXE% -m venv "%TESTIUM_VENV%"
+    IF !ERRORLEVEL! NEQ 0 (
+        echo ERROR while creating the testium venv.
+        exit /b 1
+    )
+    call "%TESTIUM_VENV%\Scripts\pip" install --quiet --upgrade pip
+    call "%TESTIUM_VENV%\Scripts\pip" install --quiet -r "%PROJECT_DIR%\src\requirements.txt"
+    REM language-server extra so `testium lsp` works from source (lsp_check.py)
+    call "%TESTIUM_VENV%\Scripts\pip" install --quiet "pygls>=1.3"
+)
+call "%TESTIUM_VENV%\Scripts\pip" install --quiet -e "%FAKE_EXPORTER%"
+SET CMD="%TESTIUM_VENV%\Scripts\python.exe" "%PROJECT_DIR%\src\testium"
+GOTO LAUNCH
 
 :MODE_WHEEL
 SET "WHEEL=%PROJECT_DIR%\dist\testium-%VERSION%-py3-none-any.whl"
@@ -115,10 +139,13 @@ IF NOT EXIST "%WHEEL_VENV%" (
     echo Creating wheel venv at %WHEEL_VENV%
     %PYTHON_EXE% -m venv --system-site-packages "%WHEEL_VENV%"
     call "%WHEEL_VENV%\Scripts\pip" install --quiet --upgrade pip
-    call "%WHEEL_VENV%\Scripts\pip" install --quiet "%WHEEL%"
+    REM install with the [lsp] extra so the wheel channel is validated in its
+    REM language-server-capable form (pulls pygls), matching `pip install testium[lsp]`.
+    call "%WHEEL_VENV%\Scripts\pip" install --quiet "%WHEEL%[lsp]"
 )
-"%WHEEL_VENV%\Scripts\python.exe" -m testium %TAIL%
-exit /b %ERRORLEVEL%
+call "%WHEEL_VENV%\Scripts\pip" install --quiet -e "%FAKE_EXPORTER%"
+SET CMD="%WHEEL_VENV%\Scripts\python.exe" -m testium
+GOTO LAUNCH
 
 :MODE_PYI
 SET "PYI_BIN=%PROJECT_DIR%\dist\testium-%VERSION%.exe"
@@ -127,5 +154,22 @@ IF NOT EXIST "%PYI_BIN%" (
     echo ERROR: PyInstaller binary not found in %PROJECT_DIR%\dist -- run build_all.sh first.
     exit /b 1
 )
-"%PYI_BIN%" %TAIL%
+SET CMD="%PYI_BIN%"
+GOTO LAUNCH
+
+REM ---------- launch ----------------------------------------------------------
+
+:LAUNCH
+echo -- launch: %CMD%
+
+REM LSP check (this exact channel): `schema` must keep its nested actions and
+REM `lsp` must answer initialize. Mirrors run.sh; aborts the run on failure.
+echo -- LSP check (%MODE%)
+"%VENV_PYTHON%" "%SCRIPT_DIR%\lsp_check.py" %CMD%
+IF !ERRORLEVEL! NEQ 0 (
+    echo ERROR: LSP check failed for mode %MODE%.
+    exit /b 1
+)
+
+%CMD% %TAIL%
 exit /b %ERRORLEVEL%