feat: initial AC telemetry Lua plugin

- CSP Lua app that reads telemetry via ac.* API
- Sends JSON over UDP to configurable target (default 127.0.0.1:5005)
- Purpose-built serializer with zero GC pressure at 60Hz
- Pre-allocated buffer tables, no per-frame allocations
- Graceful fallback when ac global is absent (testing outside AC)
- .gitignore for .idea/

README.md

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+# ACTelemetry
+
+A Custom Shaders Patch (CSP) Lua application for Assetto Corsa that reads car telemetry data via the CSP Lua API and sends it as JSON over UDP.
+
+## What It Does
+
+The plugin runs inside Assetto Corsa under Proton/Linux. It collects telemetry at 60 Hz from the CSP Lua API and broadcasts a JSON datagram to a configurable UDP endpoint each frame (throttled to the configured rate).
+
+## Installation
+
+Copy the entire `ac-telemetry-plugin` directory into your CSP Lua apps folder:
+
+```
+<Assetto Corsa root>/extension/lua/apps/
+```
+
+Enable the app in the CSP in-game app launcher.
+
+## Configuration
+
+Edit `config.lua` to set the target UDP endpoint:
+
+```lua
+local config = {
+    target_host = "127.0.0.1",   -- UDP receiver IP
+    target_port = 5005,          -- UDP receiver port
+    send_interval = 1 / 60,      -- 60 Hz send rate
+}
+```
+
+## JSON Format
+
+Each UDP datagram contains a JSON object with the following schema (sent to `target_host:target_port`):
+
+```json
+{
+  "timestamp": 1716123456.789,
+  "speed_kmh": 245.3,
+  "rpm": 8750,
+  "gear": 6,
+  "throttle": 0.85,
+  "brake": 0.0,
+  "steering": 0.12,
+  "g_forces": { "x": 0.5, "y": -0.2, "z": 1.0 },
+  "wheel_slip": [0.1, 0.1, 0.0, 0.0],
+  "suspension_travel": [0.15, 0.14, 0.16, 0.15],
+  "lap_time": 85.234,
+  "lap_count": 5
+}
+```
+
+| Field              | Type             | Description                        |
+|--------------------|------------------|------------------------------------|
+| `timestamp`        | number           | `os.clock()` time                  |
+| `speed_kmh`        | number           | Car speed in km/h                  |
+| `rpm`              | number           | Engine RPM                         |
+| `gear`             | number           | Current gear                       |
+| `throttle`         | number           | Throttle input (0.0 - 1.0)         |
+| `brake`            | number           | Brake input (0.0 - 1.0)            |
+| `steering`         | number           | Steering input (-1.0 - 1.0)        |
+| `g_forces`         | object           | G-forces: `x`, `y`, `z`            |
+| `wheel_slip`       | array[4]         | Per-wheel slip (FL, FR, RL, RR)    |
+| `suspension_travel`| array[4]         | Per-wheel suspension travel        |
+| `lap_time`         | number           | Current lap time in seconds        |
+| `lap_count`        | number           | Completed lap count                |
+
+## Dependencies
+
+- CSP (Custom Shaders Patch) with Lua support
+- LuaSocket (bundled with CSP)