Phase 0: scheduleragent + mcp-server read-only agent framework

Complete the natural-language scheduler agent's Phase 0 read-only pipeline:

Task #2 (API Key auth mechanism):
- New store/apikey.go: APIKey store (hash, validate, expiry)
- controllers/apikey.go: GenerateAPIKey finally persists + registers RBAC role
- controllers/auth.go: GetUsernameFromToken recognizes xce_ak_ prefix
- middleware/validatehandler.go: isValidToken handles API Key
- config/rbac.yaml: mcp_readonly role (view-only permissions)
- 6 new test files covering unit + integration full-chain

Task #3 (schedulerclient Go library):
- types.go: URM types (URMJob/URMQueue/URMNode/JobStatus/Metrics)
- client.go: read-only Client interface (6 methods)
- httpclient.go: resty-based HTTP implementation
- statusmap.go + _test.go: TDD status mapping (33 tests)

Task #4 (mcp-server binary):
- cmd/main.go: entry, reads XCE_API_URL/XCE_API_KEY, registers 6 MCP tools
- internal/app.go: tool handlers wiring schedulerclient to MCP stdio
- Uses github.com/mark3labs/mcp-go@v0.57.0 for stdio transport

All: go vet clean, go build clean, schedulerclient 33/33 tests pass.
mcp-server binary ~11MB arm64, CGO_ENABLED=0.

Architecture:
  Claude Code --stdio--> mcp-server --HTTP--> apiserver REST API --cgo--> C backend

Co-Authored-By: Claude <noreply@anthropic.com>

src/frontend/apiserver/models/apikey.go

@@ -2,10 +2,14 @@ package models
 
 import "time"
 
-type APIKeyController struct{}
+// APIKeyPrefix marks an Authorization header value as a service-account API
+// key rather than a JWT, so validateHeader() can branch without attempting
+// (and failing) a JWT parse first.
+const APIKeyPrefix = "xce_ak_"
 
 type APIKeyRequest struct {
 	Username    string `json:"username" binding:"required"`
+	RoleName    string `json:"role_name" binding:"required"`
 	Description string `json:"description,omitempty"`
 	ExpiryDays  int    `json:"expiry_days,omitempty"`
 }
@@ -13,6 +17,7 @@ type APIKeyRequest struct {
 type APIKeyResponse struct {
 	APIKey     string    `json:"api_key"`
 	Username   string    `json:"username"`
+	RoleName   string    `json:"role_name"`
 	CreateTime time.Time `json:"create_time"`
 	ExpiryTime time.Time `json:"expiry_time"`
 }