Upgrade Dagger from v0.19.11 to v0.20.0 (#285)

## Summary
- Bump Dagger engine version from v0.19.11 to v0.20.0 in `dagger.json`
- Pin dagger CLI to `0.20.0` in `mise.toml` (was `"latest"`)
- Regenerated `.dagger/uv.lock` (new SDK deps: httpcore, beartype bump)

## Testing
- [x] `dagger call validate-workflows --src=.` passes on v0.20.0
- [ ] CI build workflow passes

Reviewed-on: #285

mise.toml

@@ -2,4 +2,4 @@
 "pipx:ansible-core" = { version = "latest", uvx = "true", uvx_args = "--with botocore --with boto3" }
 prek = "latest"
 pulumi = "latest"
-dagger = "latest"
+dagger = "0.20.0"