M6-06: Add desktop distribution investigation

[DrunkOnJava]

Created from the roadmap audit in TODO.md.

Source: https://github.com/DrunkOnJava/rvt-rs/blob/main/TODO.md#L849
Tracking commit: 1ec8105

Scope

Labels: priority:P3, type:research, area:viewer

• Evaluate whether a Tauri/Electron wrapper is worth maintaining for
  non-technical users.
• Compare:
  • install complexity
  • file size
  • privacy
  • auto-update
  • code-signing burden

Acceptance criteria:

• Decision record under docs/decisions/.
• No desktop wrapper is started until maintenance cost is accepted.

Definition of done

• The TODO acceptance criteria for this section are implemented or explicitly superseded by a linked decision.
• Tests, fixtures, or documentation are added at the level appropriate to the change risk.
• User-facing behavior and limitations remain honest in README/docs/viewer messaging.
• Relevant CI checks pass before the issue is closed.