fix(entitlements): gate paid MCP tools (send_invoice/agi_submit/vat_declaration_submit) server-side (#846)

The HTTP routes call requireCapability at every paid chokepoint, but the
MCP/agent path bypassed the paywall entirely: the three external-service
tools stage operations whose commit calls the email / Skatteverket services
directly, with no capability check. After the 2026-07-07 trial cutover a
trial-connected non-payer using the gnubok MCP connector could still send
invoice emails and file AGI/VAT.

Close the gap with two layers, mirroring the existing TOOL_SCOPE_MAP gate:

- Dispatch gate (mcp-server/server.ts): MCP_TOOL_CAPABILITY_MAP, checked
  right after the scope check, blocks a non-entitled company before any
  pending op is staged. Emits errorKind='capability_denied' telemetry.
- Commit-time gate (commitPendingOperation): PAID_OPERATION_CAPABILITY_MAP,
  checked before the atomic claim. The real external-service chokepoint —
  applies to the MCP approve tool AND the UI approval path, and closes the
  trial-connected-token window (the grant has expired by commit time). A
  blocked op stays 'pending', so it is re-approvable once the company subscribes.

Adds a transport-free capabilityBlockedError() helper (shared bilingual
copy) and locks both maps with tests (maps, dispatch gate, commit gate).
Only the three write/submit tools are gated; SKV read/local tools stay free
per the statutory carve-out. No DB/migration change; self-hosted stays all-on.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/entitlements/has-capability.ts

@@ -80,6 +80,12 @@ export async function hasCapability(
   return true
 }
 
+/** Bilingual paywall copy, shared by every transport (HTTP route, MCP tool, commit executor). */
+export const CAPABILITY_BLOCKED_MESSAGE_SV =
+  'Den här funktionen kräver en betald prenumeration. Uppgradera för att fortsätta använda externa tjänster.'
+export const CAPABILITY_BLOCKED_MESSAGE_EN =
+  'This feature requires a paid subscription. Upgrade to keep using external services.'
+
 /**
  * Standard bilingual 403 for a capability-blocked endpoint. Matches the
  * sandbox/guard envelope so the UI surfaces the upsell consistently.
@@ -87,10 +93,8 @@ export async function hasCapability(
 export function capabilityBlockedResponse(key: CapabilityKey): NextResponse {
   return NextResponse.json(
     {
-      error:
-        'Den här funktionen kräver en betald prenumeration. Uppgradera för att fortsätta använda externa tjänster.',
-      error_en:
-        'This feature requires a paid subscription. Upgrade to keep using external services.',
+      error: CAPABILITY_BLOCKED_MESSAGE_SV,
+      error_en: CAPABILITY_BLOCKED_MESSAGE_EN,
       capability_blocked: true,
       capability: key,
     },
@@ -98,6 +102,30 @@ export function capabilityBlockedResponse(key: CapabilityKey): NextResponse {
   )
 }
 
+export interface CapabilityBlockedError {
+  code: 'capability_blocked'
+  capability_blocked: true
+  capability: CapabilityKey
+  message_sv: string
+  message_en: string
+}
+
+/**
+ * Transport-free counterpart to capabilityBlockedResponse, for call sites that
+ * don't return a NextResponse — the MCP dispatcher (folded into the JSON-RPC
+ * `isError` envelope) and the pending-operation commit executor. Same copy and
+ * the same `capability_blocked: true` marker so every surface upsells alike.
+ */
+export function capabilityBlockedError(key: CapabilityKey): CapabilityBlockedError {
+  return {
+    code: 'capability_blocked',
+    capability_blocked: true,
+    capability: key,
+    message_sv: CAPABILITY_BLOCKED_MESSAGE_SV,
+    message_en: CAPABILITY_BLOCKED_MESSAGE_EN,
+  }
+}
+
 /**
  * Convenience wrapper: check + return the 403 in one call. Returns the
  * NextResponse to return from the route, or null when the company has the