ComeOnOver Desktop Launcher v1.10.19

v1.10.19: Linux build (M1+M2 of multi-platform support)

One codebase produces a Windows .exe (full feature set) and a Linux binary
(cross-platform subset with no-op stubs where Win32/WebView2/Velopack
don't apply). 313/313 tests pass on Linux. No Windows regression.

Mechanisms:
- csproj <PackageReference Condition="'$(OS)' == 'Windows_NT'"> for
  WebView2/Velopack/System.Management/System.Drawing.Common
- csproj <Compile Remove ... Condition="'$(OS)' != 'Windows_NT'"> for
  Win32-/WMI-/Velopack-bound source files
- #if WINDOWS for the few mixed files (Program.cs, RegisterWindowsServices
  in App.axaml.cs)
- MainWindow.axaml refactored to use ContentControl placeholder; WebView
  wiring split into Windows-only MainWindow.WebView.cs partial class

11 Linux service stubs added under Services/Linux/ folders.
LinuxClaudePathResolver finds /usr/bin/claude-desktop (Debian build).
Process starts, framework initialises, MainWindowViewModel constructs,
slot monitor + seed cache updater run on their timers.

Stubbed for v1.10.19, deferred to later milestones: procfs scanner (M3),
thumbnails (Wayland), window hide/show, registry-based autostart, Velopack
auto-update, embedded usage WebView.

Files: ROADMAP.md + docs/dev/LEARNINGS.md updated.