Redesign whole-PC Stats and adopt Geist typography

[imnakul]

The Stats slide now presents whole-PC CPU and physical RAM readings plus the busiest physical GPU engine, aggregating that engine's per-process counters before reporting its utilization. Sampling runs on a one-second worker only while the Stats slide or Settings page is visible.

The collapsed notch has three readable metric groups; the expanded slide and Settings page use a composed, theme-aware overview. Stats is discoverable under NOTCH settings, where users can include it in the carousel and choose it as the resting slide. Desktop and unknown battery states are handled without inventing a charge reading.

Geist and Geist Mono are bundled from Google Fonts with their OFL licenses and source hashes. Private DirectWrite collections cover the notch, FlashScreen and edge overlays; egui uses Geist for proportional text and Geist Mono for numeric/monospaced text. Existing explicit custom font choices are preserved when migrating old defaults.

Ordinary launches now start quietly in the tray. --settings opens Settings directly, including when Venu is already running; --startup and --minimized keep their quiet behavior.

The illustrative dark-theme mockup is in docs/stats-mockup.svg; its sample readings are not measured telemetry or a Windows screenshot.

Validation:

• Windows-target source check against the actual src/main.rs using a temporary build=false manifest.
• 16 pure-function and config tests covering CPU/GPU/power math, font fallback, launch flags, config migration and Stats slide controls.
• cargo fmt --all --check and git diff --check.
• Native Windows GitHub Actions CI passed: run #36 (cargo build --locked, cargo test --locked, formatting).