docs(roadmap): mark D-04 auto-update check complete

Background update check shipped in commits 21ba029 (module),
a00fee2 (wired into startup), cbdfde4 (21 tests).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: astrapisixtynine

docs/ROADMAP.md

@@ -32,7 +32,7 @@ Lower the installation barrier for non-technical users. Simple Launcher first, T
 - [ ] D-02: Simple Launcher for macOS (.app bundle, arm64-only for initial release). CI workflow: [launcher-macos.yml](../.github/workflows/launcher-macos.yml). Same source as Windows launcher; spec file's darwin BUNDLE block produces the .app. Smoke test pending Mac hardware. Unsigned binary requires Gatekeeper bypass (right-click -> Open) on first launch. Intel Mac support (universal2) and code signing deferred until user demand.
 - [ ] D-03: Simple Launcher for Linux (PyInstaller binary via CI, smoke test pending). Same source as Windows launcher; spec file is cross-platform aware. CI workflow: [launcher-linux.yml](../.github/workflows/launcher-linux.yml). Optional follow-up: .desktop file for GNOME/KDE menu integration.
 - [ ] D-03a: AppImage for Linux — deferred. The PyInstaller binary requires `python3-tk` on the target (preinstalled on every major desktop distro). AppImage would make that self-contained at a 4-10x size cost and added CI complexity (FUSE + appimagetool). Re-evaluate only when a user reports a missing-tkinter failure in the wild.
-- [ ] D-04: auto-update check in the launcher (notify user of new versions)
+- [x] D-04: auto-update check in the launcher (notify user of new versions). Background thread polls `https://api.github.com/repos/astrapi69/bibliogon/releases/latest` on every launcher start, compares against the installed version from the manifest, and shows a non-blocking "Open release page / Dismiss" dialog when a strictly newer release is available. All failures are silent (network, timeout, rate limit, malformed response). Stdlib-only (urllib + threading). 21 tests in [test_update_check.py](../launcher/tests/test_update_check.py).
 - [ ] D-05: Full Windows installer (downloads Docker Desktop + Bibliogon repo + generates .env, no terminal required at any step). Larger scope than D-01's launcher. Defer until user feedback shows the install (not the start) is the actual friction. See [docs/explorations/desktop-packaging.md](explorations/desktop-packaging.md) for context and triggers for reconsidering.
 
 ### 2. Book and chapter templates (priority: after distribution)