[Qynl]

FabricRacers — a complete racing game inside Minecraft (1.21.1 / Fabric)

This PR replaces the previous contents of main (deleted in the first commit,
a5549ab) with an all-new mod built from scratch: FabricRacers.

What it does

• Nine cars — Go-Kart, Rally Hatch, Sport Coupe, Hypercar, Formula Racer,
  Baja Truck, Drift Machine, Hot Rod and a secret Shadow Prototype — with
  arcade-sim physics (engine curve, bike-model steering, grip limits, drag,
  handbrake slides, weight transfer, drift scoring and real crash damage).
  Cars are server-authoritative; the client only sends input.
• AI that races — spline-based racing lines, curvature braking, overtaking,
  boost on straights, handbrake rotation for drift cars, rubber-banding,
  skill-scaled mistakes, stuck recovery, and "hand your own car to the AI".
• Five stock circuits built by a real track generator, plus /race record
  to bake a lap you drove into a brand-new circuit, and a Track Wand to place
  and rotate any catalogue entry in the world (kerbs, barriers, grandstands,
  animated start gate, checkpoints, pit lane, decorations).
• A full race engine — grid, five-light countdown, lap timing, per-checkpoint
  progress, live standings, gaps, pit stops, fastest lap, DNF handling, AI
  take-over after the flag, podium ceremony with trophies and emeralds.
• Tuning + economy — seven upgrade systems (engine, gearbox, brakes, tyres,
  aero, chassis, nitro), 16 paint colours, parts and cars sold by villager
  mechanics and wandering traders, prize money, and trophies.
• Progression — per-player profiles with races, wins, podiums, laps,
  overtakes, drift points, distance, top speed, per-track bests and titles from
  Walk-on to Legend, persisted per world.
• Client experience — hand-rolled car model/renderer, race HUD (speed,
  boost, drift, laps, standings, countdown), garage screen, race-control screen
  and circuit catalogue.

Verification

CI on every push (all green):

1. tools/validate_assets.py — JSON, blockstate/model graph, textures,
   structures and translation keys.
2. ./gradlew build — compiles both source sets, produces the jar.
3. A dedicated server is booted with the mod and driven over RCON: the
   circuit catalogue is listed, modded blocks are placed, a car is summoned and
   its synched NBT read back and round-tripped, and a crowd of villagers is
   checked for the mod's trade offers.

All content is original and generated by the in-repo Python tools
(tools/gen_textures.py, tools/gen_tracks.py, tools/validate_assets.py);
regenerating is deterministic.

MIT licensed.