Fix eagle-exec deployment and simplify implementation (#5569)

- Remove sudo symlink creation (deploy user lacks passwordless sudo)
- Simplify eagle-exec to read from /opt/eagle0/.active-instance file
- Update deploy-blue-green.sh to write active instance to file
- Keep fallback to checking running containers if file doesn't exist

Users can add their own alias:
  alias eagle-exec='/opt/eagle0/scripts/eagle-exec.sh'

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

scripts/deploy-blue-green.sh

@@ -35,6 +35,7 @@ WARMUP_SCRIPT="${SCRIPT_DIR}/warmup-eagle.sh"
 SAVES_DIR="${APP_DIR}/saves"
 FLUSH_MARKER="${SAVES_DIR}/.flush_complete"
 DEPLOYMENT_IN_PROGRESS="${SAVES_DIR}/.deployment_in_progress"
+ACTIVE_INSTANCE_FILE="${APP_DIR}/.active-instance"
 
 # Colors for output
 RED='\033[0;31m'
@@ -298,6 +299,10 @@ main() {
     create_flush_marker "${deploy_id}" "eagle-${staging}"
     log_info "[DEPLOY:${deploy_id}] Flush marker created - server will auto-invalidate stale cache"
 
+    # Write active instance file for eagle-exec helper
+    echo "eagle-${staging}" > "${ACTIVE_INSTANCE_FILE}"
+    log_info "[DEPLOY:${deploy_id}] Active instance file updated: eagle-${staging}"
+
     # Update .env for admin service
     local env_file="${APP_DIR}/.env"
     if [ "$staging" = "green" ]; then