allow fx workflow dispatches

[Svector-anu]

what

add fx to the workflow_dispatch harness choices and register a focused regression test.

why

fx is already integrated through the adapter, resolver, installer, dashboard, and standardized harness contract. the manual workflow-dispatch choice list was missed when fx was added, so gh workflow run aeon.yml -f skill=narrative-tracker -f harness=fx failed with http 422 before aeon executed any code.

this is not an fx implementation or authentication change. it only makes the existing harness selectable through manual github actions dispatches.

fix

• add fx to .github/workflows/aeon.yml
• add scripts/tests/test_workflow_harness_choices.sh
• register the regression test in .github/workflows/ci-tests.yml

verification

mutation test with only the fx option removed:

rc=1
workflow_dispatch harness choices omit fx

after restoring the option:

workflow harness choice tests passed

• node scripts/validate-config.js — clean
• node --test scripts/validate-config.test.js — 14/14 passed
• bash scripts/tests/test_resolve_harness.sh — all passed
• bash scripts/tests/test_generate_harnesses_json.sh — all passed
• git diff --check — clean

real github actions proof on the fork: run 33167164883 was accepted, logged INPUT_HARNESS: fx, resolved Harness: fx, and installed fx 0.0.6.

the run then stopped at the existing credential gate because the test fork has neither AI_GATEWAY_API_KEY nor VERCEL_OIDC_TOKEN. this pr does not change credentials, authentication, schedules, models, or the default harness.