Add desktop app service and VM dev session tooling

Introduces a new `core/applications` QML/C++ module (`Nebula.Applications`) to discover `.desktop` entries, expose filterable application models, and launch installed apps safely from the shell. The desktop launcher now uses real installed apps with themed icon loading and fallback glyphs, adds output-aware surface sizing via `OutputTracker`, and wires in image/icon providers. It also adds VMware-focused Sway/shell wrapper scripts, updates Sway config/session env defaults, and refreshes README docs to document the new development flow and Desktop 0.1 behavior.

core/applications/README.md

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+# Nebula Applications
+
+Shared C++ service for discovering and launching installed Linux applications from `.desktop` entries.
+
+Desktop and the future Bigscreen shell should both use this library. It has no Desktop-specific QML.
+
+## Behaviour
+
+- Scans XDG application directories (`XDG_DATA_HOME`, `XDG_DATA_DIRS`, with the usual `~/.local/share` and `/usr/share` defaults).
+- Hides entries with `Hidden=true` or `NoDisplay=true`, and respects `OnlyShowIn` / `NotShowIn` / `TryExec`.
+- Exposes a `QAbstractListModel` to QML (`desktopId`, `name`, `genericName`, `comment`, `iconName`, `categories`, `terminal`).
+- Launches with `QProcess::startDetached` and `QProcess::splitCommand`. Does not use a shell.
+- Strips or substitutes common Exec field codes when launching without files/URLs.
+
+QML module URI: `Nebula.Applications`.
+
+See `shells/desktop/README.md` for launcher behaviour and session integration.
+