refactor: move source files to src/ directory and rename project to Captioneer

Restructure Go source code into a dedicated `src/` directory, rename the project from "audio-listen" to "Captioneer", and update README accordingly. Add `.gitignore` entry for the built binary `captioneer`.

README.md

@@ -1,4 +1,4 @@
-# audio-listen
+# Captioneer
 
 Local, live English captions for the audio playing through your default PulseAudio/PipeWire output device. It captures that output's monitor source, runs the Parakeet TDT v2 model locally, and writes captions to the terminal.
 
@@ -24,7 +24,7 @@ Clone the project, then download the required models once:
 
 ```bash
 git clone <your-repository-url>
-cd audio-listen
+cd captioneer
 ./scripts/download-models.sh
 ```
 
@@ -35,20 +35,20 @@ The download installs the Parakeet TDT v2 int8 model and Silero VAD into `models
 Use VAD mode for normal live captions. It shows a temporary `…` caption while speech is active, then prints a timestamped final caption after 0.5 seconds of silence:
 
 ```bash
-go run . --mode=vad
+go run ./src --mode=vad
 ```
 
 Use fixed mode to decode exact time slices, even through silence:
 
 ```bash
-go run . --mode=fixed --chunk-duration=1s
+go run ./src --mode=fixed --chunk-duration=1s
 ```
 
 Build a reusable executable instead of using `go run`:
 
 ```bash
-go build -o audio-listen .
-./audio-listen --mode=vad
+go build -o captioneer ./src
+./captioneer --mode=vad
 ```
 
 Press <kbd>Ctrl</kbd>+<kbd>C</kbd> to stop. Pending audio is flushed before exit.
@@ -70,17 +70,28 @@ Examples:
 
 ```bash
 # Faster fixed chunks
-go run . --mode=fixed --chunk-duration=500ms
+go run ./src --mode=fixed --chunk-duration=500ms
 
 # Fewer VAD preview redraws and four CPU threads
-go run . --mode=vad --chunk-duration=2s --threads=4
+go run ./src --mode=vad --chunk-duration=2s --threads=4
 
 # Store or reuse models outside this repository
-go run . --mode=vad --models-dir=/path/to/models
+go run ./src --mode=vad --models-dir=/path/to/models
 ```
 
 There are no environment variables to configure. All supported configuration is supplied with command-line options.
 
+## Source layout
+
+All Go code lives in `src/`. It remains one executable package, split into focused files:
+
+- `main.go` coordinates startup and shutdown.
+- `config.go` defines and validates command-line options.
+- `capture.go` reads the default system-audio monitor.
+- `audio.go` contains PCM conversion and audio calculations.
+- `models.go` validates and initializes Parakeet and Silero.
+- `captions.go` handles fixed chunks, VAD segments, and terminal output.
+
 ## Output and troubleshooting
 
 Final captions go to standard output in this form:
@@ -92,7 +103,7 @@ Final captions go to standard output in this form:
 Startup messages and overload warnings go to standard error, so you can save final captions separately:
 
 ```bash
-go run . --mode=vad > captions.txt
+go run ./src --mode=vad > captions.txt
 ```
 
 - **Missing model files:** run `./scripts/download-models.sh` again.
@@ -104,5 +115,5 @@ go run . --mode=vad > captions.txt
 
 ```bash
 go test ./...
-go build ./...
+go build -o captioneer ./src
 ```