feat(launchpad): implement secure email hashing for access control

This commit introduces a more secure method for verifying user
access to the internal launchpad by hashing email addresses.

- Replaces the plain-text email list with SHA-256 hashes.
- Adds a script to generate these hashes from `iap-users.txt`.
- Updates the launchpad HTML to hash the input email and compare
 it against the `allowed-hashes.json` file.
- Updates Makefile to generate hashes before deploy and serve.
- Adds .keep file for krow_client folder.

Makefile

@@ -124,11 +124,15 @@ build:
 
 launchpad-dev:
 	@echo "--> Starting local Launchpad server using Firebase Hosting emulator..."
+	@echo "    - Generating secure email hashes..."
+	@node scripts/generate-allowed-hashes.js
 	@firebase serve --only hosting:launchpad --project=$(FIREBASE_ALIAS)
 
 # --- Deployment ---
 deploy-launchpad-hosting:
 	@echo "--> Deploying Internal Launchpad to Firebase Hosting..."
+	@echo "    - Generating secure email hashes..."
+	@node scripts/generate-allowed-hashes.js
 	@echo "    - Target: hosting:launchpad"
 	@echo "    - Project: $(FIREBASE_ALIAS)"
 	@firebase deploy --only hosting:launchpad --project=$(FIREBASE_ALIAS)