Copy declared Flutter assets/shaders/fonts into cljd dep stubs

[dankinsoid]

Problem

sync-pubspec! mirrors every ClojureDart dependency into .clojuredart/deps/<sha256-of-pubspec>/, but it spits only the pubspec.yaml into that stub. The asset, shader and font files that pubspec declares under flutter: assets: / shaders: / fonts: are never copied in.

Dart sources are still pulled from the dependency's real checkout (~/.gitlibs or :local/root), so compilation is fine. But Flutter resolves a package's declared assets relative to that package's own pubspec.yaml directory — i.e. the stub (see flutter_tools asset.dart, which iterates package pubspecs). The declared files aren't there, so loading fails at runtime.

Concretely, a dep whose pubspec has:

flutter:
  shaders:
    - shaders/oklab_gradient.frag

ships a stub containing that declaration but not the .frag, and:

FragmentProgram.fromAsset("packages/<pkg>/shaders/oklab_gradient.frag")

throws unable to load asset at runtime. Flutter itself parses the dependency pubspecs correctly — the gap is purely that ClojureDart doesn't place the physical files in the stub.

Fix

• find-pubspec now returns [pubspec-contents base-dir] — the directory the pubspec's paths resolve against (nil for jar deps).
• When creating a stub, sync-pubspec! copies each declared asset/shader/font from that base dir into the stub. Handles plain file entries, asset directory entries (recursively), the richer {path: ...} asset form, and nested fonts: [{fonts: [{asset: ...}]}]. Copy is skipped when the target already exists; jar deps (assets live inside the archive) are unchanged.

Testing

Verified in isolation that files, shaders, asset directories, {path: ...} entries and fonts are mirrored, and that a nil base-dir (jar) and a missing source file are both no-ops rather than errors. Namespace loads clean.

This replaces a post-compile babashka script we were running to work around the missing files.