Add call graph fixtures for various languages and scenarios

- Introduced `all-edge-reasons.json` to test edge resolution reasons in .NET.
- Added `all-visibility-levels.json` to validate method visibility levels in .NET.
- Created `dotnet-aspnetcore-minimal.json` for a minimal ASP.NET Core application.
- Included `go-gin-api.json` for a Go Gin API application structure.
- Added `java-spring-boot.json` for the Spring PetClinic application in Java.
- Introduced `legacy-no-schema.json` for legacy application structure without schema.
- Created `node-express-api.json` for an Express.js API application structure.

docs/modules/cli/guides/airgap.md

@@ -2,6 +2,20 @@
 
 Offline/air-gapped usage patterns for the Stella CLI.
 
+## Offline kit commands
+- Import an offline kit (local verification + activation)
+  ```bash
+  stella offline import \
+    --bundle ./bundle-2025-12-14.tar.zst \
+    --verify-dsse \
+    --verify-rekor \
+    --trust-root /evidence/keys/roots/stella-root.pub
+  ```
+- Check current offline kit status
+  ```bash
+  stella offline status --output table
+  ```
+
 ## Prerequisites
 - CLI installed from offline bundle; `local-nugets/` and cached plugins available.
 - Mirror/Bootstrap bundles staged locally; no external network required.