Reorganize ballot question i18n into dedicated namespace

[tripledoublev]

Summary

• Creates `ballotquestions.json` as a dedicated i18n namespace consolidating all ballot question strings
• Moves 33 keys out of `search.json` (where they landed when BQ browse was first built) and 77 keys out of `common.json` (where detail-page strings lived under a nested `ballotQuestion.*` object) — 110 keys total, exact match
• Updates all 11 components in `components/ballotquestions/` and their test mocks to use the new namespace, simplifying key paths (e.g. `ballotQuestion.overview.title` → `overview.title`)
• Leaves `testimony.json` and `editProfile.json` untouched — those files contain testimony-specific and profile-specific strings that happen to reference ballot questions, and belong where they are

What was NOT changed

`testimony.json` has a `ballotQuestion` section used by `publish/` and `TestimonyCard/` components (form panel, edit button, publish flow). Those keys are testimony UI strings, not ballot question content strings, and were intentionally left in place.

Test plan

• Browse ballot questions page renders correctly (filters, status labels, question numbers, result count)
• Ballot question detail header renders type, election, court, document labels and back link
• Overview tab renders for initiative BQs
• "How the vote works" section renders correctly on 24-firearms-referendum (referendum type — the only one)
• For & Against, Synthesis, Campaign Financials, Testimonies tabs render correctly
• `BrowseBallotQuestions.test.tsx`, `CommitteeHearing.test.tsx`, `YourTestimonyPanel.test.tsx`, `BallotQuestionAlert.test.tsx`, `BallotQuestionTabLinks.test.tsx` all pass