feat: Phase 1 MVP with audit fixes — Wayland screen capture + VAAPI encoding

Phase 1 MVP implementation of wl-webrtc: Wayland screen capture tool
with hardware-accelerated VAAPI H.264 encoding and WebTransport output.

Includes all 9 runtime bug fixes from code audit (fix-audit-issues plan):

CRITICAL:
- C2: h264_metadata BSF with repeat_sps/repeat_pps in encode pipeline
- C4: FpsLimit wired as timing gate in on_copy_complete

HIGH:
- C3+A2: DRM device discovery via dmabuf feedback MainDevice event,
  unified resolve_drm_path() helper (CLI > compositor > auto > fallback)
- H2: Separate physical_size (mm) from mode_size (pixels) in wl_output
- H1+A3: Multi-output warning + named-output-not-found error

MEDIUM:
- M5: tv_sec u32->u64 to avoid Y2106 timestamp truncation
- M4: Guard against SHM Buffer event (DMA-BUF only)

Key components:
- src/avhw.rs: FFmpeg VAAPI encoder + filter graph + BSF pipeline
- src/state.rs: Wayland event loop + output negotiation + screencopy
- src/cap_wlr_screencopy.rs: wlr-screencopy capture source
- src/fps_limit.rs: Frame rate limiting with configurable target
- src/transform.rs: Frame format conversion utilities

README.md

@@ -0,0 +1,56 @@
+# wl-webrtc
+
+Wayland screen capture and encoding tool.
+
+## Prerequisites
+
+- **Rust toolchain** (1.70+): `rustup default stable`
+- **FFmpeg 6.0+** dev libraries with VAAPI support:
+  - Arch: `pacman -S ffmpeg`
+  - Ubuntu/Debian: `apt install libavcodec-dev libavformat-dev libavutil-dev libswscale-dev libva-dev`
+  - Fedora: `dnf install ffmpeg-devel libva-devel`
+- **Wayland** dev libraries:
+  - Arch: `pacman -S wayland-protocols`
+  - Ubuntu/Debian: `apt install libwayland-dev wayland-protocols`
+  - Fedora: `dnf install wayland-devel wayland-protocols-devel`
+- **DRM** dev libraries:
+  - Arch: `pacman -S libdrm`
+  - Ubuntu/Debian: `apt install libdrm-dev`
+  - Fedora: `dnf install libdrm-devel`
+
+## Build
+
+```bash
+cargo build --release
+```
+
+## Run
+
+```bash
+# Basic capture to file
+wl-webrtc --output output.mp4
+
+# With custom FPS and bitrate
+wl-webrtc --output output.mp4 --fps 60 --bitrate 8000000
+
+# Specify DRM device for hardware encoding
+wl-webrtc --output output.mp4 --drm-device /dev/dri/renderD128
+
+# Verbose mode
+wl-webrtc --output output.mp4 -v
+```
+
+## CLI Arguments
+
+| Argument | Default | Description |
+|---|---|---|
+| `-o`, `--output` | (required) | Output file path (e.g., output.mp4) |
+| `--output-name` | auto | Wayland output name to capture |
+| `--fps` | 30 | Target frames per second |
+| `--codec` | h264 | Video codec (h264 only for MVP) |
+| `--hw-accel` | vaapi | Hardware acceleration method |
+| `--drm-device` | auto | DRM render device path |
+| `--bitrate` | auto | Target bitrate in bps |
+| `--gop-size` | auto | Group of Pictures size |
+| `-v`, `--verbose` | false | Enable verbose logging |
+| `--port` | 0 | WebTransport server port (unused in MVP) |