feat(agent): ship the Go agent canvas port — eino interrupt/resume + Redis check-pointing (#16035)

Replaces the Python agent canvas runtime with a Go implementation that
runs inside `cmd/server_main`.

The canvas compiles into an eino Workflow that pauses on wait-for-user
via native Interrupt/Resume (no sentinel flag) and resumes from a
Redis-backed CheckPointStore.

All 21 Python agent components and ~35 tools are ported with functional
parity.

Sandbox providers now read their JSON config from the admin-panel
system_settings table with env fallback.

234 files / +35,413 / -6,111. All Go files are gofmt-clean (CI gate
added); drops the v2 DSL E2E step and the gap-analysis plan (both
redundant after the port ships).

## Type of change

- [x] Refactoring
- [x] New feature
- [x] Bug fix

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

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

.github/workflows/tests.yml

@@ -129,6 +129,34 @@ jobs:
             fi
           fi
 
+      - name: Check gofmt of changed Go files
+        if: ${{ github.event_name == 'pull_request' || github.event_name == 'pull_request_target' }}
+        run: |
+          CHANGED_FILES=$(git diff --name-only ${{ github.event.pull_request.base.sha }}...${{ github.event.pull_request.head.sha }} \
+            | grep -E '\.go$' || true)
+
+          if [ -n "$CHANGED_FILES" ]; then
+            echo "Check gofmt of changed Go files"
+            readarray -t files <<< "$CHANGED_FILES"
+            HAS_ERROR=0
+            for file in "${files[@]}"; do
+              if [ -f "$file" ]; then
+                if [ -z "$(gofmt -l "$file")" ]; then
+                  echo "✅ $file"
+                else
+                  echo "❌ $file (run: gofmt -w \"$file\")"
+                  HAS_ERROR=1
+                fi
+              fi
+            done
+
+            if [ $HAS_ERROR -ne 0 ]; then
+              exit 1
+            fi
+          else
+            echo "No Go files changed"
+          fi
+
       - name: Build ragflow go server
         run: |
           BUILDER_CONTAINER=ragflow_build_$(od -An -N4 -tx4 /dev/urandom | tr -d ' ')