feat: explain Linux development support in setup and settings

[enaboapps]

The Linux foundation reports unsupported Bluetooth and input, but the UI attributes this to the computer's hardware and still offers ineffective input controls. This adds Linux-specific development-build explanations, blocks setup progression while input is unavailable, and replaces input settings with an unavailable message. Windows/macOS permission flows remain intact.

Browser sample data now recognizes desktop Linux, and README documents the Ubuntu development build, visible-window behavior and remaining BlueZ work.

Stack: #711 (plan) → #714 (native foundation) → this PR. Review this diff against feat/712-linux-foundation; merge in stack order only when explicitly authorized.

Closes #713.

Validation: local frontend lint, 114 frontend tests, 5 updater-feed tests, production frontend build and whitespace check passed. Independent review of latest head 213654e85c13519d8d332d77024bc4490b4baf88 found no actionable issues. All latest-head CI checks passed: Ubuntu, Windows and macOS native checks/builds; frontend; dependency audit; CodeQL; and automated review. Native/frontend CI run.

Linux graphical sessions and physical Bluetooth hardware remain unqualified; browser preview was unavailable in this environment. Automated UI tests cover the Linux status explanations, setup gating and hidden input controls.

[greptile-apps]

Greptile Summary

The Linux development build now identifies unavailable Bluetooth and input capabilities clearly, prevents setup from continuing when native input is unavailable, and replaces ineffective pointer settings with an explanatory Controls panel. The exercised Linux UI flow confirmed that setup progression is disabled and unavailable controls are not shown.

Confidence Score: 5/5

No blocking failure remains.

The exercised Linux setup and settings flows behaved as intended: setup cannot progress without native input support, and ineffective pointer controls are unavailable.

T-Rex Logs

What T-Rex did

• Ran an isolated Vitest/jsdom frontend flow that renders the App in Linux-native state and exercised setup plus Settings Controls.
• Validated the safety work: the unsafe expectation failed due to setup Next being disabled and ineffective pointer controls, while the safe expectation passed and Linux limitation messages were recorded; the App and Settings test suites passed and lint and diff checks completed.
• Verified the before/after state behavior for the Linux-native frontend flow: the before-condition assertion failed (unsafe hypothesis), the safe-condition assertion passed with the observed state, and the executable test source was authored.
• Confirmed the repository’s relevant frontend tests passed along with TypeScript lint and whitespace-diff checks.

_{Ran code and verified through T-Rex}

_{Reviews (2): Last reviewed commit: "feat: explain Linux development limitati..." | Re-trigger Greptile}