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

.dagger/uv.lock

@@ -125,6 +125,7 @@ dependencies = [
     { name = "cattrs" },
     { name = "exceptiongroup" },
     { name = "gql", extra = ["httpx"] },
+    { name = "httpcore" },
     { name = "opentelemetry-exporter-otlp-proto-http" },
     { name = "opentelemetry-instrumentation-logging" },
     { name = "opentelemetry-sdk" },
@@ -136,10 +137,11 @@ dependencies = [
 [package.metadata]
 requires-dist = [
     { name = "anyio", specifier = ">=3.6.2" },
-    { name = "beartype", specifier = ">=0.18.2" },
+    { name = "beartype", specifier = ">=0.22.0" },
     { name = "cattrs", specifier = ">=25.1.0" },
     { name = "exceptiongroup", specifier = ">=1.3.0" },
     { name = "gql", extras = ["httpx"], specifier = ">=4.0" },
+    { name = "httpcore", specifier = ">=1.0.8" },
     { name = "opentelemetry-exporter-otlp-proto-http", specifier = ">=1.23.0" },
     { name = "opentelemetry-instrumentation-logging", specifier = ">=0.54b1" },
     { name = "opentelemetry-sdk", specifier = ">=1.23.0" },