deploy: pull app source from upstream instead of duplicating it

This repo now holds only the deploy pipeline. The application code (src,
templates, Dockerfile, pyproject, etc.) is removed and instead cloned from
the upstream repository at build time via the new SOURCE_REPO / SOURCE_REF
parameters (default: git.resf.org/documentation/rocky-man @ main). The
Docker image is built from that clone, eliminating the duplicate copy.

Also drop an accidentally committed .ruff_cache blob and ignore the
build-time clone dir and ruff cache.

Assisted-by: Claude Opus 4 (Claude Code)

.gitignore

@@ -39,8 +39,14 @@ html/
 tmp/
 .cache/
 
+# Application source cloned by the pipeline at build time
+/rocky-man/
+
 # UV cache
 .uv_cache/
 
+# Ruff cache
+.ruff_cache/
+
 # Logs
 *.log