fix: web UI and src.common bugs (wifi wrong-password, plugin icon, starlark toggle, API caching, scroll/logo/font helpers) (#646)

- wifi: keep the "wrong_password:" prefix through the restore/AP fallback so
  the UI's incorrect-password prompt fires again.
- /plugins/installed returns the manifest's icon (string only).
- /starlark/apps/<id>/toggle coerces `enabled` and delegates to
  _toggle_starlark_app (disk before memory, no KeyError, "false" is false).
- /api/v3/ JSON GETs are sent Cache-Control: no-store; non-JSON keeps 5s.
- ScrollHelper.set_scrolling_image converts non-RGB input (alpha onto black);
  create/set_scrolling_image reset last_update_time like reset_scroll.
- LogoHelper backs off a failed download per path for
  MISSING_LOGO_RECHECK_SECONDS; cleared on invalidate/clear_cache.
- refresh_placeholder_timestamp saves atomically.
- FontManager.clear_cache / _clear_plugin_font_cache bump cache_generation.
- Odds manager: per-game logs to DEBUG; JSON decode error caught before
  RequestException (same cooldown).
- element_style mangled continuations; startup validator skips null plugin
  blocks and reuses the controller's discovery.
- src/common/README lists frame_timing, json_body, render_gate.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/test_common_readme_lists_every_module.py

@@ -0,0 +1,21 @@
+"""src/common/README.md says it lists every module; keep it true.
+
+frame_timing, json_body and render_gate landed without rows, so the page a
+plugin author reads to see what core offers was missing three modules.
+"""
+
+from pathlib import Path
+
+COMMON = Path(__file__).resolve().parent.parent / "src" / "common"
+
+
+def _modules():
+    return sorted(p.stem for p in COMMON.glob("*.py") if p.stem != "__init__")
+
+
+def test_every_module_has_a_table_row_and_a_section():
+    readme = (COMMON / "README.md").read_text(encoding="utf-8")
+    missing_rows = [m for m in _modules() if f"| [`{m}`](#{m}) |" not in readme]
+    missing_sections = [m for m in _modules() if f"\n### {m}\n" not in readme]
+    assert not missing_rows, f"no summary-table row for: {missing_rows}"
+    assert not missing_sections, f"no '### <module>' section for: {missing_sections}"