fix(dashboard): show the message inside a Cloudflare tunnel error object

[HouMinXi]

Summary

• Starting a Cloudflare quick tunnel can be rejected with a structured body whose error field is an object. The endpoint page passed that object straight into new Error, so the notice rendered as [object Object] instead of the message inside it.
• The page now reads the message out of the body through the existing extractApiErrorMessage helper. A string error still shows as is, and a body with no message falls back to the previous text.

Related Issues

• Closes fix: can't create cloudflare quick tunnel (403 LOCAL_ONLY shown as [object Object]) #15294

Validation

• Change type: other (dashboard error display)
• Focused tests: vitest on cloudflared-object-error.test.tsx (1 pass) and node --import tsx/esm --test on cloudflared-object-error.node.test.ts (3 pass)
• eslint on the changed files, with the repo suppression file
• Reconciled with release/v3.8.52 @ 23a1148486
• New tests cover the change
• Defect injection: restoring new Error(data?.error || ...) makes both suites fail again, and the change was restored

Tests Added Or Updated

• src/app/(dashboard)/dashboard/endpoint/__tests__/cloudflared-object-error.test.tsx (added)
• src/app/(dashboard)/dashboard/endpoint/__tests__/cloudflared-object-error.node.test.ts (added)

Coverage Notes

• The component test mounts the page, triggers the tunnel action against an object error body, and asserts the notice shows the message and not [object Object].

Reviewer Notes

• The 403 LOCAL_ONLY is left as is. The tunnel route spawns a process, so a request that is neither loopback nor private is refused on purpose. This change only fixes what the operator sees.