app icon: owl with ear tufts (owner's ArtCraft drawing), Dock/taskbar/launcher wiring, palette docs

- assets/app-icon/: canonical SVG + light SVG, 1024 PNG, macOS runtime PNG, .icns, .ico,
  hicolor theme, LICENSE.txt and README (palette, geometry, provenance, regeneration).
- packaging/icons.sh regenerates everything with resvg, iconutil and the new `cargo xtask ico`.
- Native app sets the window icon (with_icon) and the Wayland app id; build.rs embeds the .ico
  and VERSIONINFO into filmcraft.exe on Windows (winresource, Windows-host build-dep only).
- packaging/linux/ai.storyteller.filmcraft.desktop with Icon=ai.storyteller.filmcraft.
- Web app: favicon.svg replaced by favicon.png from the same artwork; sidecars and
  ATTRIBUTION.md updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

xtask/src/ico.rs

@@ -0,0 +1,104 @@
+//! `cargo xtask ico <out.ico> <in.png>…`: pack PNG images into a Windows `.ico`.
+//!
+//! Vista and later read PNG-compressed icon entries, so each PNG is stored as is. The size comes
+//! from the PNG's IHDR chunk; 256 px is written as 0, per the ICO format.
+
+use std::path::Path;
+
+/// Width and height from a PNG's IHDR chunk.
+pub fn png_size(png: &[u8]) -> Result<(u32, u32), String> {
+    const SIG: &[u8] = b"\x89PNG\r\n\x1a\n";
+    if png.len() < 24 || &png[..8] != SIG || &png[12..16] != b"IHDR" {
+        return Err("not a PNG file".into());
+    }
+    let w = u32::from_be_bytes([png[16], png[17], png[18], png[19]]);
+    let h = u32::from_be_bytes([png[20], png[21], png[22], png[23]]);
+    Ok((w, h))
+}
+
+/// An ICO file holding `pngs`, which must be square and at most 256 px.
+pub fn pack(pngs: &[Vec<u8>]) -> Result<Vec<u8>, String> {
+    if pngs.is_empty() || pngs.len() > u16::MAX as usize {
+        return Err("need at least one PNG".into());
+    }
+    let mut out = Vec::new();
+    out.extend_from_slice(&0u16.to_le_bytes()); // reserved
+    out.extend_from_slice(&1u16.to_le_bytes()); // type: icon
+    out.extend_from_slice(&(pngs.len() as u16).to_le_bytes());
+    let mut offset = 6 + 16 * pngs.len();
+    for png in pngs {
+        let (w, h) = png_size(png)?;
+        if w != h || w == 0 || w > 256 {
+            return Err(format!("icon images must be square and at most 256 px, got {w}x{h}"));
+        }
+        let dim = if w == 256 { 0 } else { w as u8 };
+        out.extend_from_slice(&[dim, dim, 0, 0]); // width, height, palette size, reserved
+        out.extend_from_slice(&1u16.to_le_bytes()); // colour planes
+        out.extend_from_slice(&32u16.to_le_bytes()); // bits per pixel
+        out.extend_from_slice(&(png.len() as u32).to_le_bytes());
+        out.extend_from_slice(&(offset as u32).to_le_bytes());
+        offset += png.len();
+    }
+    for png in pngs {
+        out.extend_from_slice(png);
+    }
+    Ok(out)
+}
+
+pub fn run(args: &[&str]) -> Result<(), String> {
+    let [out, inputs @ ..] = args else {
+        return Err("usage: cargo xtask ico <out.ico> <in.png>…".into());
+    };
+    let pngs = inputs.iter().map(|p| std::fs::read(p).map_err(|e| format!("read {p}: {e}"))).collect::<Result<Vec<_>, _>>()?;
+    let ico = pack(&pngs)?;
+    std::fs::write(Path::new(out), &ico).map_err(|e| format!("write {out}: {e}"))?;
+    println!("{out}: {} images, {} bytes", pngs.len(), ico.len());
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn fake_png(size: u32) -> Vec<u8> {
+        let mut v = b"\x89PNG\r\n\x1a\n\0\0\0\x0dIHDR".to_vec();
+        v.extend_from_slice(&size.to_be_bytes());
+        v.extend_from_slice(&size.to_be_bytes());
+        v.extend_from_slice(&[8, 6, 0, 0, 0, 1, 2, 3, 4]);
+        v
+    }
+
+    #[test]
+    fn packs_directory_and_payloads() {
+        let a = fake_png(16);
+        let b = fake_png(256);
+        let ico = pack(&[a.clone(), b.clone()]).unwrap();
+        assert_eq!(&ico[..6], &[0, 0, 1, 0, 2, 0]);
+        // Entry 0: 16 px at offset 6 + 32.
+        assert_eq!(&ico[6..8], &[16, 16]);
+        assert_eq!(u32::from_le_bytes(ico[14..18].try_into().unwrap()), a.len() as u32);
+        assert_eq!(u32::from_le_bytes(ico[18..22].try_into().unwrap()), 38);
+        // Entry 1: 256 px stored as 0, right after the first payload.
+        assert_eq!(&ico[22..24], &[0, 0]);
+        assert_eq!(u32::from_le_bytes(ico[34..38].try_into().unwrap()), 38 + a.len() as u32);
+        assert_eq!(&ico[38..38 + a.len()], &a[..]);
+        assert_eq!(&ico[38 + a.len()..], &b[..]);
+    }
+
+    #[test]
+    fn rejects_bad_input() {
+        assert!(pack(&[]).is_err());
+        assert!(pack(&[fake_png(512)]).is_err());
+        assert!(pack(&[b"GIF89a".to_vec()]).is_err());
+        assert_eq!(png_size(&fake_png(48)).unwrap(), (48, 48));
+    }
+
+    #[test]
+    fn committed_icon_is_valid() {
+        let path = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../assets/app-icon/filmcraft.ico");
+        let Ok(ico) = std::fs::read(&path) else { return };
+        assert_eq!(&ico[..4], &[0, 0, 1, 0]);
+        let n = u16::from_le_bytes([ico[4], ico[5]]) as usize;
+        assert!(n >= 4, "expected several sizes in {}", path.display());
+    }
+}

xtask/src/main.rs

@@ -11,8 +11,11 @@
 //! - `fixtures [crate…]`: pre-generate the ffmpeg fixture matrix of the oracle tests (runs each
 //!   crate's ignored `generate_fixtures` test, i.e. the same generators the tests use) and print
 //!   what was made, reused or skipped.
+//! - `ico <out.ico> <in.png>…`: pack PNGs into a Windows `.ico` (used by `packaging/icons.sh`).
 //! - `ci`: fmt check, clippy -D warnings, tests, layers, assets, wasm.
 
+mod ico;
+
 use std::process::{Command, ExitCode};
 
 use serde_json::Value;
@@ -346,6 +349,7 @@ fn serve_dir(dir: &std::path::Path, port: u16) -> Result<(), String> {
                 "js" => "text/javascript",
                 "wasm" => "application/wasm",
                 "svg" => "image/svg+xml",
+                "png" => "image/png",
                 "json" => "application/json",
                 "mp4" => "video/mp4",
                 "webm" => "video/webm",
@@ -435,7 +439,11 @@ fn main() -> ExitCode {
         "ci" => ci(),
         "bench-playback" => bench_playback(),
         "web" => web(&std::env::args().skip(2).collect::<Vec<_>>()),
-        _ => Err("usage: cargo xtask <layers|assets|wasm|web [--dev] [--serve PORT]|fixtures [crate…]|ci|bench-playback [args]>".into()),
+        "ico" => {
+            let rest: Vec<String> = std::env::args().skip(2).collect();
+            ico::run(&rest.iter().map(String::as_str).collect::<Vec<_>>())
+        }
+        _ => Err("usage: cargo xtask <layers|assets|wasm|web [--dev] [--serve PORT]|fixtures [crate…]|ico OUT IN…|ci|bench-playback [args]>".into()),
     };
     match r {
         Ok(()) => ExitCode::SUCCESS,