Issue/310 title limit client side

[maxachis]

Summary

• Adds a maxLength: 255 client-side validator to the title field on the data request
  creation form, so users get immediate feedback instead of a generic API error when
  exceeding the limit
• Extracts INPUT_NAMES, SELECT_OPTS, and SCHEMA from create.vue into _constants.js for
  testability and reuse
• Adds unit tests verifying the title field's maxLength and required validators

Closes #310

Test plan

• Unit tests pass (npm run test:unit) — 32/32 passing
• Build succeeds (npm run build)
• Manual: navigate to data request creation form, enter a title longer than 255
  characters, confirm the validation message "Title must be 255 characters or fewer."
  appears before submission

[joshuagraber]

Looks good, but I think e2e is a better strategy for validating this with testing.

[joshuagraber]

I don't know that a test on constants is useful here. The validator logic is tested in design system, the constant should be its own source of truth. I think we'd get more value from end-to-end test validation if we want to ensure that the error message that shows up in the working system is what we expect.

[maxachis]

Looks good, but I think e2e is a better strategy for validating this with testing.

@joshuagraber Excellent point! We do have e2e/data-request/create.spec.js . Do you think that's sufficient as-is?

[joshuagraber]

Do you think that's sufficient as-is?

I think so, @maxachis, but if not, we can certainly add or update those test cases to ensure they're covering everything.