Phase 1 bug fixes: JAVA_HOME, CATALINA_HOME, and gradle initBundle retry

[mirandastephane]

Summary

This PR resolves all three critical bug fixes from the 2026 maintenance window
(Phase 1 of the Course Launcher Tool improvement plan).

Changes

ENBT-4103 · Fix JAVA_HOME not persisting between terminal sessions

• .sh: appends JAVA_HOME and PATH update to ~/.bashrc, ~/.zshrc, and
  ~/.profile after Zulu JRE install — idempotent, only if not already present.
• .ps1: persists JAVA_HOME and appends $ZuluPath\bin to user-scope PATH
  via SetEnvironmentVariable — idempotent check before writing.
• Both scripts print a hint to open a new terminal for changes to take effect.

ENBT-4104 · Fix missing CATALINA_HOME after gradle initBundle

• .sh: dynamically locates bundles/tomcat-* after initBundle and exports
  CATALINA_HOME for the current session. Persists to .bashrc, .zshrc,
  and .profile (idempotent).
• .ps1: same discovery via Get-ChildItem -Filter tomcat-*. Sets
  $env:CATALINA_HOME for the session and persists to user scope via
  SetEnvironmentVariable.

ENBT-4105 · Fix invalid checksum on gradle initBundle (slow connections)

• Wraps gradle initBundle in a retry loop (up to 3 attempts) on both scripts.
• Cleans bundles/ and .gradle/ cache between retries.
• Detects verifyBundle/checksum keywords and shows a specific message;
  falls back to a generic message for other errors.
• .sh: uses set +e / tee / PIPESTATUS for live streaming + exit code capture.
• .ps1: uses & + Tee-Object -Variable for zero-buffering live output and
  $LASTEXITCODE for exit code detection.

Testing

• ENBT-4103: Tested on clean machine (no Java) — JAVA_HOME persists after
  reopening terminal on Linux, Mac, and Windows.
• ENBT-4104: Server starts without "CATALINA_HOME not defined" error after
  running the script.
• CENBT-4105: Simulated slow/interrupted connection — script retries and
  displays correct messages.