Wire legacy desktop frontend menu actions to Desktop 2.0 pills instead of injecting commands

Follow-up to #1013.

Rather than injecting Open-Folders / DevTools / Restart / Reinstall / Server-Config style commands into the ComfyUI frontend menu (the terminal-style stopgap injection approach), have the ComfyUI frontend menu entries trigger the Desktop 2.0 launcher **pills** to open the relevant native pages (folders, server config, logs, updates, etc.).

Rationale: we are likely changing desktop behavior anyway, and the launcher already owns this chrome in the multi-install manager model. Driving the existing native pills from frontend menu actions is cleaner than replicating each command inside the embedded web UI.

## Scope
- Proper feature-flag path in core + frontend (mirroring the terminal/downloads flag pattern) so the frontend can signal the host to open a given native page.
- Map the legacy desktop electronAdapter menu actions (Open Logs/Models/Output/Input/Custom Nodes folder, Open extra_model_paths.yaml, Open DevTools, Server Config, Restart/Reinstall/Check for Updates) to launcher pills/native pages where they make sense for Desktop 2.0.
- Supersedes the per-command JS injection approach for these elements.

## Out of scope (tracked separately)
- Terminal access (already shipped + supports_terminal PRs).
- Model downloads injection + feature flag (#1027).