Updated Timer with Broad RPi Compatibility and kernel 6.x GPIO support

[larsll]

Issue: #14

Description of changes:

• All RPi models now supported: RPi 1/2/3/4/5, Zero W, Zero 2W, and all Compute Modules (CM1–CM5)
• Replaced rpi-gpio with node-libgpiod as the primary GPIO library — uses the /dev/gpiochipN character device interface, unaffected by the kernel 6.x sysfs GPIO renumbering that broke rpi-gpio on Bookworm
• rpi-gpio retained as optional fallback for pre-kernel-6.x systems only
• Automatic chip detection: RPi 5 / CM5 use gpiochip4; all other models use gpiochip0
• Recommended OS updated to Raspberry Pi OS Bookworm (32-bit or 64-bit depending on device); Bullseye and earlier not recommended
• Activation script now uses uname -m architecture detection (aarch64 / armv7l / armv6l) instead of fragile model-string matching, correctly covering all RPi variants
• ARMv6 devices (RPi Zero W, RPi 1, CM1) use unofficial Node.js builds from unofficial-builds.nodejs.org
• Node.js updated to v18.20.8 LTS; libgpiod-dev and node-libgpiod installed unconditionally
• Conditional UFW rule: opens port 8080/tcp if ufw is installed and active
• Server-side timestamps: lap time captured at GPIO trigger using Date.now(), eliminating network latency from measurements
• Per-sensor debounce tracking, configurable via config.gpio.debounceMs (default 2000ms)
• Configuration now defined entirely in the config object at the top of timer.js — no external config file
• WebSocket messages now send structured JSON lap data (timestamp, GPIO pin, lap number, per-sensor count) instead of a plain 'lap' string; updated racePage.tsx and racePageLite.tsx to match
• package.json bumped to v2.0.0; node-libgpiod and rpi-gpio moved to optionalDependencies; engines: { node: ">=18.0.0" } added
• Zip command updated to exclude package-lock.json; README updated with OS table, Node.js install steps, NTP sync guidance, configuration reference, and troubleshooting section

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[larsll]

@StevenAskwith @davidfsmith This one is ready for review. Will need some testing on different devices before merging. (I have tested on Pi Zero W and RPi5 CM so far...)