feat: add prototype syncing for local dev and AI context

This commit introduces a new feature to synchronize prototypes
from an external repository for local development and to provide
context for AI tools.

- Added `make sync-prototypes` target to Makefile to build and
 copy prototypes from the adjacent 'client-krow-poc' repository.
- Added `.geminiignore` entries to prevent Gemini from ignoring
 prototypes, ensuring they are available for context.
- Added `.gitignore` entries to ignore generated prototype files,
 except for the `.keep` files, to keep the directories.
- Added `04-sync-prototypes.md` documentation to explain how to
 sync prototypes.
- Removed empty `internal/prototypes/.keep` file.

makefiles/tools.mk

@@ -1,8 +1,12 @@
 # --- Development Tools ---
 
-.PHONY: install-git-hooks
+.PHONY: install-git-hooks sync-prototypes
 
 install-git-hooks:
 	@echo "--> Installing Git hooks..."
 	@ln -sf ../../scripts/git-hooks/pre-push .git/hooks/pre-push
 	@echo "✅ pre-push hook installed successfully. Direct pushes to 'main' and 'dev' are now blocked."
+
+sync-prototypes:
+	@echo "--> Synchronizing prototypes from external repository..."
+	@./scripts/sync-prototypes.sh