feat: runtime controls, configurable audio format, README, UX polish

- Add runtime key bindings: [/] drop-off, ,/. log scaling, -/+ sensitivity
- Add --fps named flag (was positional), --rate and --channels CLI args
- Fix version string to auto-read from Cargo.toml
- Graceful error when pw-record is not found
- Add README with usage table, input mode examples, runtime controls
- Improve arg help text with ranges and clearer descriptions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -0,0 +1,74 @@
+# spectrust
+
+A terminal audio spectrum analyzer written in Rust. Visualizes PCM audio in real time using block characters — reads from PipeWire, a file, or stdin.
+
+```
+▁▂▃▄▅▆▇█▇▆▅▄▃▂▁▁▂▃▄▅▆▇█▇▆▅▄▃▂▁▁▂▃▄▅▆▇█
+```
+
+## Installation
+
+**Arch Linux (AUR)**
+```
+yay -S spectrust
+```
+
+**From source**
+```
+cargo install --path .
+```
+
+Requires Rust 1.70+. PipeWire (`pw-record`) is only needed for the `-p` capture mode.
+
+## Usage
+
+```
+spectrust [OPTIONS]
+```
+
+| Option | Default | Description |
+|--------|---------|-------------|
+| `-f, --fps <N>` | `60` | Target frames per second |
+| `-p, --pipewire` | — | Capture audio directly from PipeWire |
+| `-i, --input <FILE>` | — | Read PCM from a file (stdin if omitted) |
+| `-l, --log-power <N>` | `1.4` | Frequency scaling power (0.5–3.0); higher values give more space to bass |
+| `-d, --drop-off <N>` | `0.75` | Bar drop-off factor per frame (0.0 = instant, 1.0 = no drop) |
+| `--rate <HZ>` | `48000` | Sample rate — must match the audio source |
+| `--channels <N>` | `2` | Channel count — must match the audio source |
+
+### Input modes
+
+**PipeWire** — capture system audio directly:
+```
+spectrust -p
+```
+
+**stdin** — pipe from any recorder:
+```
+pw-record --format=s16 --rate=48000 --channels=2 --raw - | spectrust
+arecord -f S16_LE -r 48000 -c 2 | spectrust
+```
+
+**File** — replay a raw PCM file:
+```
+spectrust -i recording.pcm
+```
+
+### Runtime controls
+
+| Key | Action |
+|-----|--------|
+| `q` / `Ctrl+C` | Quit |
+| `[` / `]` | Decrease / increase drop-off speed |
+| `,` / `.` | Decrease / increase log frequency scaling |
+| `-` / `+` | Decrease / increase sensitivity |
+
+## Notes
+
+- Input is expected as signed 16-bit little-endian PCM (s16le). This matches `pw-record --format=s16 --raw` and `arecord -f S16_LE`.
+- If `--rate` or `--channels` don't match the actual source the visualization will be distorted.
+- The sensitivity control scales bar heights at render time; it has the most noticeable effect on quiet signals.
+
+## License
+
+MIT