feat: initialize K-Shrink workspace with multiple crates for image shrinking utility

- Add Cargo.toml for workspace configuration with dependencies.
- Create README.md with project description, usage, and architecture details.
- Implement `bin` crate for the main executable, including clipboard processing logic.
- Add `config` crate for handling configuration in TOML format.
- Develop `lib` crate containing core image processing logic and error handling.
- Introduce `platform` crate for platform-specific clipboard interactions, starting with Wayland.
- Implement tests for image shrinking functionality and clipboard interactions.

crates/config/src/lib.rs

@@ -0,0 +1,228 @@
+use serde::Deserialize;
+use std::path::PathBuf;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum ConfigError {
+    #[error("Failed to parse config: {0}")]
+    ParseError(String),
+    #[error("Quality must be 0–100, got {0}")]
+    InvalidQuality(u8),
+    #[error("poll_ms must be at least 100, got {0}")]
+    InvalidPollMs(u64),
+}
+
+/// Output format for compressed images.
+///
+/// ## Lossy (quality applies)
+/// - `jpeg`    — Best for photos. `quality` controls compression (80 is a good default).
+/// - `avif`    — Modern format, better than JPEG at same quality. `quality` applies.
+///
+/// ## Lossless (quality ignored)
+/// - `webp`    — Best for screenshots/UI. Usually smaller than PNG.
+/// - `png`     — Universal lossless. No size reduction vs source PNG.
+/// - `qoi`     — Fast lossless. Usually larger than PNG but faster to encode/decode.
+/// - `farbfeld`— Simple 16-bit lossless. Rarely needed.
+/// - `tiff`    — Lossless TIFF. Large files, used in professional workflows.
+/// - `gif`     — Lossless but only 256 colors. Avoid for photos.
+/// - `hdr`     — Radiance HDR floating-point format.
+/// - `openexr` — OpenEXR high dynamic range.
+///
+/// ## Uncompressed (will be larger than source PNG)
+/// - `bmp`, `tga`, `pnm`, `ico`
+#[derive(Debug, Deserialize, Clone, Copy, PartialEq, Eq)]
+#[serde(rename_all = "lowercase")]
+pub enum OutputFormat {
+    Jpeg,
+    Avif,
+    Webp,
+    Png,
+    Qoi,
+    Farbfeld,
+    Tiff,
+    Gif,
+    Hdr,
+    #[serde(rename = "openexr")]
+    OpenExr,
+    Bmp,
+    Tga,
+    Pnm,
+    Ico,
+}
+
+impl From<OutputFormat> for lib::OutputFormat {
+    fn from(f: OutputFormat) -> Self {
+        match f {
+            OutputFormat::Jpeg     => lib::OutputFormat::Jpeg,
+            OutputFormat::Avif     => lib::OutputFormat::Avif,
+            OutputFormat::Webp     => lib::OutputFormat::Webp,
+            OutputFormat::Png      => lib::OutputFormat::Png,
+            OutputFormat::Qoi      => lib::OutputFormat::Qoi,
+            OutputFormat::Farbfeld => lib::OutputFormat::Farbfeld,
+            OutputFormat::Tiff     => lib::OutputFormat::Tiff,
+            OutputFormat::Gif      => lib::OutputFormat::Gif,
+            OutputFormat::Hdr      => lib::OutputFormat::Hdr,
+            OutputFormat::OpenExr  => lib::OutputFormat::OpenExr,
+            OutputFormat::Bmp      => lib::OutputFormat::Bmp,
+            OutputFormat::Tga      => lib::OutputFormat::Tga,
+            OutputFormat::Pnm      => lib::OutputFormat::Pnm,
+            OutputFormat::Ico      => lib::OutputFormat::Ico,
+        }
+    }
+}
+
+#[derive(Debug, Deserialize, Clone)]
+pub struct GeneralConfig {
+    /// Output format. See [`OutputFormat`] for details.
+    /// Default: `webp`
+    #[serde(default = "default_format")]
+    pub format: OutputFormat,
+
+    /// Compression quality 0–100. Only used when `format = "jpeg"`.
+    /// Ignored for `webp` (always lossless) and `png` (always lossless).
+    /// Default: `80`
+    #[serde(default = "default_quality")]
+    pub quality: u8,
+
+    /// How often to check the clipboard, in milliseconds.
+    /// Lower values are more responsive but use more CPU.
+    /// Minimum: 100. Default: `500`
+    #[serde(default = "default_poll_ms")]
+    pub poll_ms: u64,
+}
+
+fn default_format() -> OutputFormat {
+    OutputFormat::Webp
+}
+
+fn default_quality() -> u8 {
+    80
+}
+
+fn default_poll_ms() -> u64 {
+    500
+}
+
+impl Default for GeneralConfig {
+    fn default() -> Self {
+        Self {
+            format: default_format(),
+            quality: default_quality(),
+            poll_ms: default_poll_ms(),
+        }
+    }
+}
+
+#[derive(Debug, Deserialize, Clone)]
+pub struct Config {
+    #[serde(default)]
+    pub general: GeneralConfig,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            general: GeneralConfig::default(),
+        }
+    }
+}
+
+fn validate(config: Config) -> Result<Config, ConfigError> {
+    if config.general.quality > 100 {
+        return Err(ConfigError::InvalidQuality(config.general.quality));
+    }
+    if config.general.poll_ms < 100 {
+        return Err(ConfigError::InvalidPollMs(config.general.poll_ms));
+    }
+    Ok(config)
+}
+
+pub fn config_path() -> PathBuf {
+    dirs::config_dir()
+        .unwrap_or_else(|| PathBuf::from("."))
+        .join("k-shrink")
+        .join("config.toml")
+}
+
+pub fn load_config() -> Result<Config, ConfigError> {
+    let path = config_path();
+    if !path.exists() {
+        return Ok(Config::default());
+    }
+    let text = std::fs::read_to_string(&path)
+        .map_err(|e| ConfigError::ParseError(e.to_string()))?;
+    let config: Config =
+        toml::from_str(&text).map_err(|e| ConfigError::ParseError(e.to_string()))?;
+    validate(config)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_config_format_webp_quality_80() {
+        let c = Config::default();
+        assert_eq!(c.general.format, OutputFormat::Webp);
+        assert_eq!(c.general.quality, 80);
+        assert_eq!(c.general.poll_ms, 500);
+    }
+
+    #[test]
+    fn parse_valid_toml() {
+        let toml = r#"
+[general]
+format = "jpeg"
+quality = 75
+poll_ms = 200
+"#;
+        let c: Config = toml::from_str(toml).unwrap();
+        assert_eq!(c.general.format, OutputFormat::Jpeg);
+        assert_eq!(c.general.quality, 75);
+        assert_eq!(c.general.poll_ms, 200);
+    }
+
+    #[test]
+    fn missing_file_returns_default() {
+        let path = PathBuf::from("/tmp/definitely_does_not_exist_k_shrink.toml");
+        let result = if !path.exists() {
+            Ok(Config::default())
+        } else {
+            load_config()
+        };
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().general.quality, 80);
+    }
+
+    #[test]
+    fn invalid_toml_returns_error() {
+        let bad = "not valid [ toml {{";
+        let result: Result<Config, _> =
+            toml::from_str(bad).map_err(|e| ConfigError::ParseError(e.to_string()));
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn invalid_quality_returns_error() {
+        let c = Config {
+            general: GeneralConfig {
+                format: OutputFormat::Webp,
+                quality: 200,
+                poll_ms: 500,
+            },
+        };
+        assert!(matches!(validate(c), Err(ConfigError::InvalidQuality(200))));
+    }
+
+    #[test]
+    fn poll_ms_too_low_returns_error() {
+        let c = Config {
+            general: GeneralConfig {
+                format: OutputFormat::Webp,
+                quality: 80,
+                poll_ms: 50,
+            },
+        };
+        assert!(matches!(validate(c), Err(ConfigError::InvalidPollMs(50))));
+    }
+}