fix(cli): resolve bundled icons at runtime so icons setup works in release builds

[angelodibella]

Problem

wayle icons setup is broken in every packaged build. It locates the bundled icons with a compile-time path (env!("CARGO_MANIFEST_DIR")/../resources/...), which in CI-built release binaries bakes in the runner's workspace:

$ wayle icons setup
Error: Resources directory not found: /__w/wayle/wayle/wayle/../resources/icons/hicolor/scalable/actions

This fails even though the release archive ships the icons right next to the binary, and it means packaged installs (release tarball, AUR wayle-bin) have no way to install or refresh the bundled set.

The practical fallout is worse than a failed command: users who set up icons under an older version and then upgraded across the grappa v1 → v2 icon format change are left with stale stroke-based v1 SVGs on disk, which a v2-era shell renders as filled-in silhouettes (bluetooth rune with its counters filled, night-light reduced to a dot) — with no supported way to fix it.

Fix

Resolve the resources directory at runtime, first existing candidate wins:

1. <exe_dir>/icons/hicolor/scalable/actions — extracted release-archive layout
2. /usr/share/wayle/… and /usr/local/share/wayle/… — distro packages that install the shipped icons/ directory
3. the CARGO_MANIFEST_DIR path — development builds (cargo run from a checkout), unchanged behavior

On no match, the error now lists every searched location instead of one baked-in path.

Testing

• cargo check / cargo clippy -p wayle clean, cargo fmt applied
• From a source checkout (candidate 3): installs all 361 bundled icons (verified against a sandboxed XDG_DATA_HOME)
• Simulated release layout — binary copied beside an icons/ tree (candidate 1): resolves exe-relative and installs
• Real-world validation: manually applying the equivalent copy on an AUR wayle-bin 0.7.0 install fixed the mangled-icon rendering described above

Note for packagers

With candidate 2 in place, distro packages can simply install the release archive's icons/ directory to /usr/share/wayle/ and wayle icons setup will find it (the AUR wayle-bin PKGBUILD currently drops the icons/ directory entirely — I'll flag that to its maintainer separately).