fix(functional-tests): skip v2 pairing specs when the stack serves v1

[fxa-agent]

Because

• The v2 pairing specs ran, and failed, against a stack that serves pairing.version 1.
• The specs did not check the served version. pairChoice.spec.ts already does.

This pull request

• Reads the served version once in beforeAll in pairingFlowV2.spec.ts, with browser and target, as pairChoice.spec.ts does. Each test skips when the version is not 2.
• The skip path builds no Marionette browser.
• Reads the served version in the existing beforeEach of pairingFlowV2Android.spec.ts and pairingFlowV2iOS.spec.ts, after the env and Nightly gates. Both skip the same way.
• The skip message names the served version.
• pairingUnsupported.spec.ts is unchanged. It does not read the pairing config.
• No v1 test changes.

Issue that this pull request solves

Closes: FXA-14637

Checklist

Put an x in the boxes that apply

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).
• I have manually reviewed all AI generated code.

How to review (Optional)

• Key files/areas to focus on: the beforeAll and beforeEach in pairingFlowV2.spec.ts.
• Suggested review order: pairingFlowV2.spec.ts, then the Android and iOS specs.
• Risky or complex parts: none.

Screenshots (Optional)

Not applicable. No user interface change.

Other information (Optional)

Local run on a stack that serves version 1. FIREFOX_BINARY=/bin/true gets past the Nightly gate.

• npx playwright test tests/pairing/pairingFlowV2.spec.ts --project=local: 3 tests skipped, Needs the stack to serve config.pairing.version=2 (serving 1). The same run on the old spec tried to launch Marionette and failed with Marionette port 2829 not available after 30000ms.
• pairChoice.spec.ts: 4 passed, 3 skipped (its own v2 tests).
• The Android and iOS specs skip on the local stack at their env gates.
• Lint, Prettier and tsc on the changed files: pass. tsc reports errors on main in lib/testAccountTracker.ts, not in the changed files.
• Not run: a stack that serves version 2 with Firefox Nightly. CI covers it.