refactor: replace swe-rex with native Modal SDK for Modal backend (#3538)

Drop the swe-rex dependency for Modal terminal backend and use the
Modal SDK directly (Sandbox.create + Sandbox.exec). This fixes:

- AsyncUsageWarning from synchronous App.lookup() in async context
- DeprecationError from unencrypted_ports / .url on unencrypted tunnels
  (deprecated 2026-03-05)

The new implementation:
- Uses modal.App.lookup.aio() for async-safe app creation
- Uses Sandbox.create.aio() with 'sleep infinity' entrypoint
- Uses Sandbox.exec.aio() for direct command execution (no HTTP server
  or tunnel needed)
- Keeps all existing features: persistent filesystem snapshots,
  configurable resources (CPU/memory/disk), sudo support, interrupt
  handling, _AsyncWorker for event loop safety

Consistent with the Docker backend precedent (PR #2804) where we
removed mini-swe-agent in favor of direct docker run.

Files changed:
- tools/environments/modal.py - core rewrite
- tools/terminal_tool.py - health check: modal instead of swerex
- hermes_cli/setup.py - install modal instead of swe-rex[modal]
- pyproject.toml - modal extra: modal>=1.0.0 instead of swe-rex[modal]
- scripts/kill_modal.sh - grep for hermes-agent instead of swe-rex
- tests/ - updated for new implementation
- environments/README.md - updated patches section
- website/docs - updated install command

scripts/kill_modal.sh

@@ -2,7 +2,7 @@
 # Kill all running Modal apps (sandboxes, deployments, etc.)
 #
 # Usage:
-#   bash scripts/kill_modal.sh          # Stop swe-rex (the sandbox app)
+#   bash scripts/kill_modal.sh          # Stop hermes-agent sandboxes
 #   bash scripts/kill_modal.sh --all    # Stop ALL Modal apps
 
 set -uo pipefail
@@ -17,10 +17,10 @@ if [[ "${1:-}" == "--all" ]]; then
         modal app stop "$app_id" 2>/dev/null || true
     done
 else
-    echo "Stopping swe-rex sandboxes..."
-    APPS=$(echo "$APP_LIST" | grep 'swe-rex' | grep -oE 'ap-[A-Za-z0-9]+' || true)
+    echo "Stopping hermes-agent sandboxes..."
+    APPS=$(echo "$APP_LIST" | grep 'hermes-agent' | grep -oE 'ap-[A-Za-z0-9]+' || true)
     if [[ -z "$APPS" ]]; then
-        echo "  No swe-rex apps found."
+        echo "  No hermes-agent apps found."
     else
         echo "$APPS" | while read app_id; do
             echo "  Stopping $app_id"
@@ -30,5 +30,5 @@ else
 fi
 
 echo ""
-echo "Current swe-rex status:"
-modal app list 2>/dev/null | grep -E 'State|swe-rex' || echo "  (none)"
+echo "Current hermes-agent status:"
+modal app list 2>/dev/null | grep -E 'State|hermes-agent' || echo "  (none)"