[Go Support] Go web framework adapters for API endpoint detection (Gin, Echo, net/http)

[KanishkThamman]

Expected Behavior

NuGuard detects HTTP route handlers in Go web frameworks (Gin, Echo,
net/http) and emits API_ENDPOINT nodes with chat_payload_key,
auth_required, and request_body_schema metadata — the same metadata
populated by nuguard/sbom/adapters/python/fastapi_adapter.py and
nuguard/sbom/adapters/python/flask_adapter.py for Python applications.
This allows the redteam stage to auto-discover AI chat endpoints.

Current Behavior

Go HTTP servers wrapping LLM calls produce no API_ENDPOINT nodes, so the
redteam executor has no target endpoint to probe even when the SBOM correctly
identifies the underlying model.

Possible Solution

Create nuguard/sbom/adapters/go/http_server.py as a GoFrameworkAdapter
subclass covering:

1. Gin (github.com/gin-gonic/gin) — detect router.POST("/path", handler)
   and router.GET("/path", handler) calls; inspect the handler function body
   for c.ShouldBindJSON(&req) to infer the request body type.
2. Echo (github.com/labstack/echo) — detect e.POST("/path", handler)
   and similar patterns.
3. net/http — detect http.HandleFunc("/path", handler) and
   mux.Handle("/path", ...) patterns.

For each route, emit an API_ENDPOINT node. Attempt to resolve prompt field
names from the bound struct (mirroring _PROMPT_FIELD_NAMES in
fastapi_adapter.py, line 70). Emit an AUTH node when middleware like
gin.BasicAuth() or JWT middleware is detected.

Steps to Reproduce (for bugs)

N/A — this is a feature addition.

Context

Part of #172 (Add Golang Support to NuGuard Pipeline).
Depends on sub-issues 1, 2, and 3.