feat(logging): add diagnostic crash log subsystem

[f1rep0wr]

Summary

The launcher ships as a PyInstaller --windowed --onefile exe, so every existing print(...) writes to a stdout that doesn't exist and uncaught exceptions on Qt threads or in discord_game_sdk.dll die silently. This PR adds a stdlib-logging-based diagnostic subsystem so end-user bug reports become actionable, and migrates every existing print site to it.

• New logger.py — RotatingFileHandler at data/logs/launcher.log (1 MB × 5), sys.excepthook + threading.excepthook + faulthandler.enable, session preamble (version/Python/platform/CWD/argv), 3-tier path fallback (<cwd>/data/logs → %LOCALAPPDATA% → %TEMP%), atexit cleanup of the faulthandler FD, RLock-guarded idempotency. A username-redaction filter runs on every log record so the file is shareable publicly.
• print → logging migration across functions.py / mech_editor.py / discord_rpc.py / run.py. log.exception(...) inside except blocks so the full traceback lands on disk. Filesystem-sourced strings (filenames, paths) formatted with %r to defeat log injection via planted filenames.
• show_error_box and prompt_for_new_game_folder — _error_count increment moved adjacent to the dialog so a logging or Tk failure can never bump the counter without the user actually seeing the dialog (preserves the invariant InjectionThread at run.py:29 relies on).
• run.py — adds an "Open Log File" IconButton that opens launcher.log in Notepad (deliberately not Explorer — spawning Explorer from a --uac-admin process is a documented UAC escalation surface). Adds a Session end (close). log line in closeEvent and removes a pre-existing duplicate self.rpc_manager.stop() call at the old run.py:307.
• constants.py — new LAUNCHER_VERSION = "1.0.8" constant consumed by the log preamble; must stay in sync with version.txt's filevers tuple when bumping.

What this looks like for end users

1. A new icon under the Discord and Info icons. Same IconButton widget already used for the Info button. Placed at (10, 95) directly below it. If data/assets/log.png exists it's used; otherwise the widget renders its existing fallback (a primary-green bordered circle with a bold "L" letter, matching how the Info button falls back to "i" today). Tooltip on hover: "Open diagnostic log".

2. Clicking it opens launcher.log in Notepad. Two branches in _open_log_file (run.py:158-179):

• Normal case (logging initialized + file exists on disk) → subprocess.Popen(["notepad.exe", log_path]). The user sees Notepad open with the full log.
• Fallback case (logging never initialized, or the file is missing) → a plain QMessageBox.information saying "The diagnostic log has not been created yet, or the launcher failed to initialize logging. Check %TEMP%\e710-launcher-boot.log for clues if this is unexpected." This is deliberately QMessageBox.information, not show_error_box, because using the latter would bump _error_count from a benign UI affordance and taint the next CONNECT cycle.

3. Every existing error dialog now ends with a "Diagnostic logs folder:" footer. This goes through the modified show_error_box (functions.py). The footer is appended via a lazy from logger import get_log_dir so the dialog still renders even if logging is uninitialized (in which case no footer is appended — graceful degradation). End users filing a bug now have a path to copy + paste from without being told where to look.

4. Log file content is publicly shareable. The username-redaction filter rewrites every record (message, args, and materialized exception tracebacks) so paths like C:\Users\<actual-name>\AppData\Local\... become C:\Users\<user>\AppData\Local\... before they hit disk. Users can attach launcher.log directly to a Discord message or GitHub issue without scrubbing it first. faulthandler.log (native crash file) only contains the "armed at" timestamp markers under normal operation — no memory addresses or DLL paths leak.

Test plan

• python -m py_compile on every touched file
• Idempotency: setup_logging() called twice in one process keeps len(root.handlers) == 1; concurrent calls from 4 threads also produce 1 handler with no PermissionError
• Fallback chain: marking data/logs/launcher.log read-only triggers fallback to %LOCALAPPDATA%\E-710 Launcher\logs
• Privacy: scanned the produced launcher.log after a session + an artificially raised PermissionError with a home-directory path — zero occurrences of the actual Windows username
• _error_count invariant: monkey-patched tk.Tk to raise, called prompt_for_new_game_folder, confirmed counter stays at 0 when no dialog could be shown
• Hooks fire end-to-end: log.exception(...) writes a traceback; raising in a worker thread triggers threading.excepthook; preamble + all log levels land in the file
• UI verified live on a dev machine: launcher boots, triggers show_antivirus_warning on a missing msvcp140.dll, the error dialog now ends with "Diagnostic logs folder:\nC:\projects\cgw-launcher\data\logs" — confirming the new footer is wired correctly through the lazy logger.get_log_dir import