test(ci): restore global fetch in shared vitest setup

[ToadAid]

Summary

Tighten shared Vitest fetch cleanup so cross-test fetch leakage is cleaned up without breaking intentional suite-level fetch setup.

What changed

Updated:

• test/setup.ts

The shared test bootstrap now:

• snapshots globalThis.fetch at the start of each test
• restores globalThis.fetch to that per-test starting value after each test

Why this patch

A broad macOS CI failure pattern pointed to shared test-state leakage. One proven leak vector was manual globalThis.fetch mutation across suites.

The first bootstrap fix restored fetch to the process-original value, but that was too blunt for suites that intentionally install a fetch mock in beforeAll.

This refined version preserves suite-level setup while still cleaning up per-test leakage.

Scope

Changed only:

• test/setup.ts

Did not change:

• product/runtime code
• Mirror status code
• suite-local logic
• workflows
• packaging

Behavior

No product behavior changed.

This is a shared test-bootstrap isolation fix only.

Validation

Passed:

• pnpm vitest run src/cli/program.nodes-media.test.ts
• pnpm vitest run src/telegram/send.test.ts src/telegram/fetch.test.ts

Result:

• program.nodes-media passed (9 tests)
• telegram/send + telegram/fetch passed (62 tests)

Notes

This patch is intentionally narrow:

• it fixes a proven shared leak point
• it preserves intentional suite-scoped fetch mocks
• it avoids broad test harness refactors

Other possible shared isolation seams may still exist, but they are out of scope for this patch.