feat(editor-v2): wire data-editor-language attrs into three textareas

Templates:
- blueprint_detail.html:52 — config textarea gets
  data-editor-language="srccfg".
- overlay_detail.html:25 — script textarea gets
  data-editor-language="bash".
- overlay_detail.html files-modal — content textarea gets
  data-editor-language="auto"; new <select data-editor-language-select>
  (auto / srccfg / bash / plain); filename input gets
  data-editor-filename.
- Both templates {% include "_editor_assets.html" %} before
  {% endblock %}.

Tests (TDD red-green):
- test_blueprint_get_includes_editor_markup pins srccfg + bundle + glue
  in blueprint detail GET.
- test_script_overlay_detail_carries_editor_markup pins bash + bundle
  + glue in script overlay GET.
- Files-modal markup verified end-to-end in Task 14 Playwright (its
  pytest fixtures are heavyweight; not worth duplicating for a static
  markup assertion).

Fast suite stays at 564 passed (no regressions).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

l4d2web/l4d2web/templates/blueprint_detail.html

@@ -49,7 +49,7 @@
         <pre class="config-preview" aria-label="Auto-loaded overlay configs">{% for o in exposed %}exec {{ o.name }}.cfg
 {% endfor %}</pre>
         {% endif %}
-        <textarea name="config" rows="8" spellcheck="false">{{ config_lines | join('\n') }}</textarea>
+        <textarea name="config" rows="8" spellcheck="false" data-editor-language="srccfg">{{ config_lines | join('\n') }}</textarea>
       </div>
     </label>
     <button type="submit">Save blueprint</button>
@@ -92,4 +92,5 @@
   </div>
 </dialog>
 <script src="{{ url_for('static', filename='js/blueprint-overlay-picker.js') }}" defer></script>
+{% include "_editor_assets.html" %}
 {% endblock %}

l4d2web/l4d2web/templates/overlay_detail.html

@@ -22,7 +22,7 @@
   <form method="post" action="/overlays/{{ overlay.id }}/script" class="stack">
     <input type="hidden" name="csrf_token" value="{{ session.get('csrf_token', '') }}">
     <label>Bash script
-      <textarea name="script" rows="20" spellcheck="false">{{ overlay.script or "" }}</textarea>
+      <textarea name="script" rows="20" spellcheck="false" data-editor-language="bash">{{ overlay.script or "" }}</textarea>
     </label>
     <p class="muted">Runs sandboxed against the overlay directory mounted at <code>/overlay</code>.</p>
     {% if not latest_build_is_running %}
@@ -168,14 +168,23 @@
   <div class="modal-body">
     <label class="files-editor-field">
       <span class="files-field-label">Filename</span>
-      <input type="text" class="files-editor-filename" autocomplete="off" spellcheck="false">
+      <input type="text" class="files-editor-filename" data-editor-filename autocomplete="off" spellcheck="false">
     </label>
     <p class="files-editor-rename-hint" hidden>↻ Save will rename <code class="files-rename-from"></code> → <code class="files-rename-to"></code>.</p>
 
     <div class="files-editor-text">
+      <label class="files-editor-field files-editor-language-field">
+        <span class="files-field-label">Language</span>
+        <select data-editor-language-select aria-label="Editor language">
+          <option value="auto">auto (from filename)</option>
+          <option value="srccfg">srccfg (.cfg)</option>
+          <option value="bash">bash (.sh)</option>
+          <option value="plain">plain</option>
+        </select>
+      </label>
       <label class="files-editor-field">
         <span class="files-field-label">Content</span>
-        <textarea class="files-editor-content" rows="14" spellcheck="false"></textarea>
+        <textarea class="files-editor-content" rows="14" spellcheck="false" data-editor-language="auto"></textarea>
       </label>
       <div class="files-editor-meta muted">
         <span class="files-editor-byte-count">UTF-8 · 0 bytes</span>
@@ -273,4 +282,5 @@
 
 <script src="{{ url_for('static', filename='js/files-overlay.js') }}" defer></script>
 {% endif %}
+{% include "_editor_assets.html" %}
 {% endblock %}

l4d2web/tests/test_blueprints.py

@@ -453,3 +453,19 @@ def test_blueprint_config_form_post_round_trip(user_client) -> None:
     # line round-tripped into the rendered textarea.
     for line in ("// pinned by form-contract test", "sv_cheats 0", "exec server.cfg"):
         assert line in body, f"line not found in rendered page: {line!r}"
+
+
+def test_blueprint_get_includes_editor_markup(user_client) -> None:
+    """Blueprint detail page must carry the editor opt-in attribute and
+    the editor asset partial — the v2 CodeMirror 6 wiring contract."""
+    create = user_client.post(
+        "/blueprints",
+        data={"name": "editor-attrs", "arguments": "", "config": "", "overlay_ids": []},
+        headers={"X-CSRF-Token": "test-token"},
+    )
+    assert create.status_code == 302
+    page = user_client.get(create.headers["Location"])
+    body = page.get_data(as_text=True)
+    assert 'data-editor-language="srccfg"' in body
+    assert "vendor/editor.bundle.js" in body
+    assert "js/editor.js" in body

l4d2web/tests/test_script_overlay_routes.py

@@ -277,3 +277,16 @@ def test_permissions_admin_can_edit_any(app, alice_id, admin_id) -> None:
     with session_scope() as s:
         overlay = s.query(Overlay).filter_by(id=overlay_id).one()
         assert overlay.script == "echo admin"
+
+
+def test_script_overlay_detail_carries_editor_markup(app, alice_id) -> None:
+    """Script overlay detail page must carry the editor opt-in attribute
+    and the editor asset partial — the v2 CodeMirror 6 wiring contract."""
+    overlay_id = _create_script_overlay(app, alice_id)
+    client = _client_for(app, alice_id)
+    response = client.get(f"/overlays/{overlay_id}")
+    assert response.status_code == 200
+    body = response.get_data(as_text=True)
+    assert 'data-editor-language="bash"' in body
+    assert "vendor/editor.bundle.js" in body
+    assert "js/editor.js" in body