fix(authz): scope import, approvals, activity, and heartbeat routes (#3315)

## Thinking Path

> - Paperclip orchestrates AI agents and company-scoped control-plane
actions for zero-human companies.
> - This change touches the server authz boundary around company
portability, approvals, activity, and heartbeat-run operations.
> - The vulnerability was that board-authenticated callers could cross
company boundaries or create new companies through import paths without
the same authorization checks enforced elsewhere.
> - Once that gap existed, an attacker could chain it into higher-impact
behavior through agent execution paths.
> - The fix needed to harden every confirmed authorization gap in the
reported chain, not just the first route that exposed it.
> - This pull request adds the missing instance-admin and company-access
checks and adds regression tests for each affected route.
> - The benefit is that cross-company actions and new-company import
flows now follow the same control-plane authorization rules as the rest
of the product.

## What Changed

- Required instance-admin access for `new_company` import preview/apply
flows in `server/src/routes/companies.ts`.
- Required company access before approval decision routes in
`server/src/routes/approvals.ts`.
- Required company access for activity creation and heartbeat-run issue
listing in `server/src/routes/activity.ts`.
- Required company access before heartbeat cancellation in
`server/src/routes/agents.ts`.
- Added regression coverage in the corresponding server route tests.

## Verification

- `pnpm --filter @paperclipai/server exec vitest run
src/__tests__/company-portability-routes.test.ts
src/__tests__/approval-routes-idempotency.test.ts
src/__tests__/activity-routes.test.ts
src/__tests__/agent-permissions-routes.test.ts`
- `pnpm --filter @paperclipai/server typecheck`
- Prior verification on the original security patch branch also included
`pnpm build`.

## Risks

- Low code risk: the change is narrow and only adds missing
authorization gates to existing routes.
- Operational risk: the advisory is already public, so this PR should be
merged quickly to minimize the public unpatched window.
- Residual product risk remains around open signup / bootstrap defaults,
which was intentionally left out of this patch because the current
first-user onboarding flow depends on it.

## Model Used

- OpenAI GPT-5 Codex coding agent with tool use and local code execution
in the Codex CLI environment.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after
screenshots
- [ ] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

Co-authored-by: Forgotten <forgottenrunes@protonmail.com>

server/src/routes/companies.ts

@@ -24,7 +24,7 @@ import {
   logActivity,
 } from "../services/index.js";
 import type { StorageService } from "../storage/types.js";
-import { assertBoard, assertCompanyAccess, getActorInfo } from "./authz.js";
+import { assertBoard, assertCompanyAccess, assertInstanceAdmin, getActorInfo } from "./authz.js";
 
 export function companyRoutes(db: Db, storage?: StorageService) {
   const router = Router();
@@ -48,6 +48,17 @@ export function companyRoutes(db: Db, storage?: StorageService) {
     return parsed;
   }
 
+  function assertImportTargetAccess(
+    req: Request,
+    target: { mode: "new_company" } | { mode: "existing_company"; companyId: string },
+  ) {
+    if (target.mode === "new_company") {
+      assertInstanceAdmin(req);
+      return;
+    }
+    assertCompanyAccess(req, target.companyId);
+  }
+
   async function assertCanUpdateBranding(req: Request, companyId: string) {
     assertCompanyAccess(req, companyId);
     if (req.actor.type === "board") return;
@@ -160,18 +171,14 @@ export function companyRoutes(db: Db, storage?: StorageService) {
 
   router.post("/import/preview", validate(companyPortabilityPreviewSchema), async (req, res) => {
     assertBoard(req);
-    if (req.body.target.mode === "existing_company") {
-      assertCompanyAccess(req, req.body.target.companyId);
-    }
+    assertImportTargetAccess(req, req.body.target);
     const preview = await portability.previewImport(req.body);
     res.json(preview);
   });
 
   router.post("/import", validate(companyPortabilityImportSchema), async (req, res) => {
     assertBoard(req);
-    if (req.body.target.mode === "existing_company") {
-      assertCompanyAccess(req, req.body.target.companyId);
-    }
+    assertImportTargetAccess(req, req.body.target);
     const actor = getActorInfo(req);
     const result = await portability.importBundle(req.body, req.actor.type === "board" ? req.actor.userId : null);
     await logActivity(db, {