Add Forgejo template variable expansion for automatic repo customization

Replace hardcoded TODO markers with Forgejo template variables (${REPO_NAME},
${REPO_OWNER}, etc.) so new repos created from this template are auto-customized.
Use Forgejo Actions context variables in build.yaml for dynamic FORGE_URL.
Hardcode forge.eblu.me as the Forgejo instance. Update CLAUDE.md and README.md
to reflect reduced manual setup steps.

Python class names kept as manual TODO (same as directory rename) since template
variables in Python code positions aren't valid syntax for linters.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dagger.json

@@ -1,6 +1,5 @@
 {
-  "_comment": "TODO: Rename 'project-template-ci' to match your project",
-  "name": "project-template-ci",
+  "name": "${REPO_NAME}-ci",
   "engineVersion": "v0.19.11",
   "sdk": {
     "source": "python"