Reject focused tests in continuous integration

Summary

Make GocciaTestRunner reject focused test.only / describe.only registrations by default when it detects a continuous-integration environment.

Why

Focused tests are useful during local development, but a committed .only can silently turn a full CI run into a passing subset. CI should fail loudly instead of producing a false-green result.

Current behavior

GocciaTestRunner already detects common CI environments in IsContinuousIntegration, but uses that signal only to disable snapshot updates. Focused registrations are selected in Goccia.Builtins.TestingLibrary.pas without a CI guard.

A current-main reproduction exits successfully while skipping the ordinary test:

printf '%s\n' 'test("ordinary", () => { expect(1).toBe(1); }); test.only("focused", () => { expect(1).toBe(1); });' | CI=true ./build/GocciaTestRunner - --no-progress --output=json

The result reports two registered tests, one passed test, one skipped test, and exit status 0.

Expected behavior

• In a detected CI environment, fail with a non-zero exit status when any focused test or suite is registered.
• Identify the focused test/suite names and source files in the diagnostic.
• Apply the guard in interpreter and bytecode modes, including serial and --jobs runs.
• Provide an explicit --allow-only escape hatch for intentional CI diagnostics.

Scope notes

• Local .only behavior remains unchanged unless CI is detected.
• Do not add a separate source linter or broaden CI-provider detection beyond the existing helper as part of this issue.
• This closes a runner-policy gap left by the focused-registration work in #118 and the parent API issue #114.

Start with GocciaTestRunner.IsContinuousIntegration and the focused-registration logic in Goccia.Builtins.TestingLibrary.pas. Run the CI=true reproduction from the issue, then check interpreter, bytecode, serial, and --jobs paths. Done means focused registrations fail CI with names and source files, while --allow-only permits intentional runs and local behavior remains unchanged.