Expose gateway billing flows from the synced server baseline

The preserved local work adds PopiNewAPI billing checkout, gateway account binding, and matching web console/pricing surfaces on top of the current test-server baseline. During the merge, the start-end video helpers from the deployed baseline were kept alongside the actionGenerate prompt handling from the WIP.

Constraint: Current usable baseline is 7054436, already deployed on the test server.

Rejected: Commit the WIP before syncing the baseline | would have hidden conflicts with the deployed start-end-frame changes.

Confidence: medium

Scope-risk: broad

Directive: Do not deploy this commit to the test server without rechecking gateway credentials and billing checkout behavior in that environment.

Tested: go test ./...

Tested: make build

Tested: cd web && npm run build

internal/server/types.go

@@ -12,18 +12,23 @@ type user struct {
 }
 
 type session struct {
-	Token       string
-	UserID      string
-	UpstreamKey string
-	User        user
-	CreatedAt   time.Time
-	ExpiresAt   time.Time
+	Token              string
+	UserID             string
+	UpstreamKey        string
+	GatewayUserID      int
+	GatewayAccessToken string
+	User               user
+	CreatedAt          time.Time
+	ExpiresAt          time.Time
 }
 
 type authSessionView struct {
-	User              user   `json:"user"`
-	SessionKey        string `json:"session_key,omitempty"`
-	UpstreamKeyMasked string `json:"upstream_key_masked,omitempty"`
+	User                     user   `json:"user"`
+	SessionKey               string `json:"session_key,omitempty"`
+	UpstreamKeyMasked        string `json:"upstream_key_masked,omitempty"`
+	GatewayUserID            int    `json:"gateway_user_id,omitempty"`
+	GatewayAccessTokenMasked string `json:"gateway_access_token_masked,omitempty"`
+	GatewayBound             bool   `json:"gateway_bound"`
 }
 
 type skill struct {
@@ -138,3 +143,16 @@ type model struct {
 	Capabilities []string       `json:"capabilities"`
 	Pricing      map[string]any `json:"pricing"`
 }
+
+type billingPlan struct {
+	ID          string   `json:"id"`
+	ProductType string   `json:"product_type"`
+	Badge       string   `json:"badge"`
+	Name        string   `json:"name"`
+	Price       string   `json:"price"`
+	Cadence     string   `json:"cadence"`
+	Summary     string   `json:"summary"`
+	Features    []string `json:"features"`
+	CTA         string   `json:"cta"`
+	Highlight   bool     `json:"highlight,omitempty"`
+}