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.

firebase.json

@@ -11,6 +11,7 @@
       "public": "firebase/internal-launchpad",
       "ignore": [
         "firebase.json",
+        "iap-users.txt",
         "**/.*",
         "**/node_modules/**"
       ]