refactor: reorganize monolithic main package into focused packages

Move the executable entry point to `src/cmd/captioneer` and split audio, capture, config, caption, and model logic into separate packages under `src/`. Update README with new build/run commands and a package-overview section.

README.md

@@ -35,19 +35,19 @@ 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 ./src --mode=vad
+go run ./src/cmd/captioneer --mode=vad
 ```
 
 Use fixed mode to decode exact time slices, even through silence:
 
 ```bash
-go run ./src --mode=fixed --chunk-duration=1s
+go run ./src/cmd/captioneer --mode=fixed --chunk-duration=1s
 ```
 
 Build a reusable executable instead of using `go run`:
 
 ```bash
-go build -o captioneer ./src
+go build -o captioneer ./src/cmd/captioneer
 ./captioneer --mode=vad
 ```
 
@@ -70,27 +70,27 @@ Examples:
 
 ```bash
 # Faster fixed chunks
-go run ./src --mode=fixed --chunk-duration=500ms
+go run ./src/cmd/captioneer --mode=fixed --chunk-duration=500ms
 
 # Fewer VAD preview redraws and four CPU threads
-go run ./src --mode=vad --chunk-duration=2s --threads=4
+go run ./src/cmd/captioneer --mode=vad --chunk-duration=2s --threads=4
 
 # Store or reuse models outside this repository
-go run ./src --mode=vad --models-dir=/path/to/models
+go run ./src/cmd/captioneer --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:
+All Go code lives in `src/` as focused packages:
 
-- `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.
+- `cmd/captioneer` is the executable entrypoint.
+- `config` defines command-line options.
+- `audio` contains PCM conversion and audio calculations.
+- `capture` reads the default system-audio monitor.
+- `models` owns Parakeet and Silero model resources.
+- `captions` handles fixed chunks, VAD segments, and terminal output.
 
 ## Output and troubleshooting
 
@@ -103,7 +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 ./src --mode=vad > captions.txt
+go run ./src/cmd/captioneer --mode=vad > captions.txt
 ```
 
 - **Missing model files:** run `./scripts/download-models.sh` again.
@@ -115,5 +115,5 @@ go run ./src --mode=vad > captions.txt
 
 ```bash
 go test ./...
-go build -o captioneer ./src
+go build -o captioneer ./src/cmd/captioneer
 ```