Guard against missing Obsidian credentials to prevent startup hang

ob login blocks waiting for interactive input when OBSIDIAN_EMAIL or
OBSIDIAN_PASSWORD is empty. Check required env vars before attempting
login to skip sync gracefully with a warning instead of hanging.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

startup.sh

@@ -8,6 +8,9 @@ mkdir -p /app/data/obsidian
 
 # Start continuous Obsidian sync if enabled
 if [ "${OBSIDIAN_CONTINUOUS_SYNC}" = "true" ]; then
+    if [ -z "${OBSIDIAN_EMAIL}" ] || [ -z "${OBSIDIAN_PASSWORD}" ] || [ -z "${OBSIDIAN_VAULT_ID}" ]; then
+        echo "WARNING: OBSIDIAN_EMAIL, OBSIDIAN_PASSWORD, or OBSIDIAN_VAULT_ID not set. Skipping sync."
+    else
         echo "Setting up Obsidian sync..."
 
         VAULT_PATH="${OBSIDIAN_VAULT_PATH:-/app/data/obsidian}"
@@ -25,6 +28,7 @@ if [ "${OBSIDIAN_CONTINUOUS_SYNC}" = "true" ]; then
         else
             echo "WARNING: Obsidian sync setup failed. Continuing without sync."
         fi
+    fi
 fi
 
 echo "Starting application..."