fix: make manual fan control safe and predictable

[naufaldi]

What Change

• Keep Manual mode selected across telemetry refreshes by separating hardware hydration from user interaction state.
• Auto-apply the stable slider target after a 2-second countdown; a new slider movement resets the countdown, and Auto cancels it.
• Replace the Apply and Restore Auto buttons with immediate Auto restoration plus inline countdown/verification status.
• Add a safe-range RPM ruler with 100 RPM ticks, 500 RPM labels, and exact range endpoints.
• Enforce temperature-aware Manual limits in both Svelte and Rust: block missing telemetry, block Manual at 95°C, and prevent RPM reductions at 85°C or hotter.
• Bump package, Cargo, Tauri, and lockfile versions to 0.1.0-beta.6.

Why Change

• Telemetry polling previously re-applied the backend Auto mode and overwrote a user’s Manual selection.
• A deliberate 2-second settling window prevents transient slider positions from reaching the SMC.
• Backend validation is required because frontend safety checks alone can be bypassed or become stale before the hardware write.
• Numeric scale marks make the requested fan speed understandable before it is applied.

Impact

• Affected areas: Fan control pane, dashboard temperature data flow, global fan-control command validation, browser/component regression tests, and release version metadata.
• Breaking changes: No public command names changed; set_all_fans_constant_rpm(rpm) and restore_all_fans_auto() remain the Tauri API.
• Dependencies: No new dependencies or schema changes.
• Testing: pnpm biome:check; pnpm test (63 tests); pnpm exec svelte-check --tsconfig ./tsconfig.json; pnpm build; pnpm playwright:test (6 tests); cargo fmt --check; cargo check; cargo clippy -- -D warnings; cargo test (124 executed, 3 hardware-dependent ignored); cargo check --target x86_64-apple-darwin; release workflow shell tests. Visual proof captured locally at the configured 960×540 Tauri size in /tmp/fanguard-beta6-ui.png.