refactor: standardize T4 on Electron and React

[wolfiesch]

Outcome

Makes Electron plus the React renderer the sole primary desktop product and prepares the v0.1.31 stabilization candidate.

What changed

• Removes the Flutter application, duplicate scripts, CI lanes, and release authority.
• Archives historical Flutter migration material.
• Makes the public demo use the same React renderer as Electron.
• Aligns product docs, development commands, release metadata, and compatibility contracts.
• Hardens the real process-boundary workspace fixture timeout.
• Adds an evidence-backed sprint plan and parity tracker.

Local proof

• pnpm check
• full 16-workspace test graph
• full build graph
• 32 Playwright scenarios
• 49 packaging contract tests
• bounded 10k-history and 20-drop reconnect soak
• unsigned v0.1.31 arm64 DMG and ZIP build
• ZIP inspection: 956 ASAR entries and executable arm64 t4-host plus OMP runtimes
• exact v0.1.31 app bundle launched with native macOS chrome, connected to Local OMP, and loaded the live 1,000-session inventory and host controls

Exact-head CI

Final head f353845 passed core, Android debug, tooling, cluster, official OMP proof on Linux x64, Linux arm64, and macOS arm64, legacy bridge continuity, and aggregate verify.

Proof boundary

This draft does not publish a release or tag. Protected signing/notarization, Linux installed launch, physical Android and Tailnet Safari smoke, and a deliberate real prompt round trip remain release-candidate evidence.

PR #144 overlaps the site deployment workflow and release consistency surfaces. If it lands first, this branch must rebase and preserve its production-cluster deployment while retaining the React demo and no-Flutter product authority.