v1.2.0 - waycentral

Add libwaycentral + waycentral.h, fix memory bugs

- Expose all modules as a shared/static library with a public header
  (waycentral.h) and pkg-config file; the binary builds on top of it
- Fix heap overflows (calendar, CPU JSON with many cores, hotspot sscanf)
- Fix overlapping sprintf UB and leaks on every tick in all modules
- Fix division by zero without a battery / swap / full_design
- Use statx() for root birth instead of spawning stat every second
- Parse /proc/meminfo per line, report real Shmem as Shared
- Library code returns errors instead of calling exit()
- Escape JSON/Pango in strings from sysfs and create_ap.conf
- Implement -v/--version, reject unknown arguments
- Makefile: separate release/debug objects, DESTDIR/PREFIX install
- Workflow: replace deprecated set-output, allow manual dispatch
- Bump version to 1.2.0

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>