fix: harden fan control release build

[naufaldi]

What Change

• Added separate direct-distribution and TestFlight/App Store build paths, including tauri.direct.conf.json, tauri.testflight.conf.json, TestFlight entitlements, and package scripts for direct and TestFlight builds.
• Hardened fan-control command handling so constant RPM, sensor-based mode, auto mode, tray actions, and snapshots share safer backend state flow.
• Added immediate fan-control sensor snapshot overlay and active preset sync after fan-control changes.
• Added privileged-helper packaging support behind a helper-binary Cargo feature and helper binary lookup/install improvements.
• Replaced the hello-world E2E with a fan-control regression that sets Fan 0 to 5000 RPM and returns it to auto.
• Added component/unit coverage for fan-control controls, distribution behavior, updater behavior, Tauri command wrappers, and a gated real-hardware fan-control smoke script.
• Updated release/signing docs, CI/release workflow commands, and native macOS UI/design documentation.

Why Change

• The beta needed a shareable install path while keeping TestFlight/App Store builds away from private macOS APIs and privileged fan-control writes.
• The fan-control UI could appear to accept a custom RPM while the backend did not prove the target RPM actually applied.
• A local immediate-refresh path could freeze after changing RPM because fan-control commands held state locks while triggering snapshot refresh.
• The new flow returns an error when SMC target RPM readback does not match the requested value instead of silently treating the write as successful.
• The new mocked E2E flow covers the reported 5000 RPM path so future regressions are easier to catch.

Impact

• Affected areas: macOS Tauri backend commands, SMC writer verification, privileged helper packaging, tray fan controls, fan-control modal/pane UI, TestFlight/direct release configs, CI/release workflows, and fan-control regression tests.
• Breaking changes: No user-facing API breaking changes. Build commands changed: direct builds should use pnpm tauri:build:direct; TestFlight/CI builds use pnpm tauri:build:testflight.
• Dependencies: Cargo feature flags added: app-store and helper-binary. No new npm runtime dependency added.
• Testing: Passed locally: cargo test fan_control_write_helper_releases_locks_before_snapshot_refresh; cargo test target_verification_failure_returns_error; rtk pnpm test (43 tests); rtk pnpm playwright:test (1 E2E); cd src-tauri && rtk cargo test (114 passed, 3 ignored); cd src-tauri && rtk cargo test --features helper-binary (115 passed, 3 ignored); rtk pnpm biome:check (42 files checked). Hardware smoke was not run because it writes real SMC fan settings and is intentionally gated behind FANGUARD_HARDWARE_SMOKE=1.
• Screenshot/browser evidence: The fan-control flow was verified through Playwright rather than a saved screenshot because the key regression is command completion/state update after changing RPM.