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/internal-launchpad/allowed-hashes.json

@@ -0,0 +1,5 @@
+[
+  "1b2e22bdec8f6493bf71ee535b6db6b4b5cd2d373f0ffb25524e229f3b5b7f5f",
+  "e075ff357ef35be2d55b0e383d59c5256980c492ada7ab84c84b2bb5ac26a73f",
+  "994b31c1aef3d59fe59bc3b8e1dec860a6fb3c73cbf41bdf45028e2c1ecbcf7a"
+]