test: add unit tests for localizedDescription selection logic

[Queen-T16]

Summary

Closes #799 — [Testing] Add unit tests for localizedDescription selection logic.

src/utils/localizedDescription.ts had no test coverage for its locale-selection / fallback behavior. This PR adds a unit-test suite and fixes a small fallback bug it exposed: an empty translation for the requested locale was returned as "" instead of falling back to the default locale.

Changes

src/utils/localizedDescription.ts

• getLocalizedDescription() now uses map[locale] || map["en"] || description instead of ??. Because parse() stores trimmed values, an empty / whitespace-only translation is represented as "", so ?? (nullish coalescing) let the empty string through. The logical-or treats missing and empty translations identically, both falling back to the default locale (English), then to the raw description string. (Verified compatible with the existing consumer in CauseDetailClient.tsx, which then runs isBlankMarkdown.)

src/__tests__/utils/localizedDescription.test.ts (new)

• getLocalizedDescription:
  • returns the requested locale's description when it exists
  • returns plain text as-is when there are no language markers
  • falls back to the default locale when the requested locale is missing
  • falls back to the default locale when the requested locale is empty (e.g. [lang:fr] / [lang:fr] with no text)
  • falls back to the raw description when the default locale is also empty
• encodeLocalizedDescription:
  • encodes translations into the [lang:xx]... marker format
  • omits empty / whitespace-only translations
  • returns "" when there are no non-empty translations
• round-trip test: encode → decode returns the correct per-locale text

Note: placed at src/__tests__/utils/localizedDescription.test.ts (the repo's existing convention, e.g. exportCsv.test.ts) rather than the literal src/tests/ path from the issue, since the repo has no src/tests directory and Jest ignores only the root tests/ e2e dir.

Acceptance criteria

• Add src/tests/utils/localizedDescription.test.ts (see note above — added under src/__tests__/utils/ per repo convention).
• Cover the case where the requested locale's description exists.
• Cover fallback to the default locale when the requested locale's description is missing or empty.

Verification

• New suite: 9 tests pass (npx jest src/__tests__/utils/localizedDescription.test.ts).
• eslint clean and prettier --check clean on both touched files.
• tsc --noEmit shows only the pre-existing errors in CauseDetailClient.tsx / WalletContext.tsx (unrelated, present on main).

Out of scope

Adding a translation UI for campaign descriptions (explicitly out of scope in the issue).

[sshdopey]

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[davidmaronio]

nice tight PR: the ?? to || change correctly makes an empty translation fall back to english (and the parse-trims-values reasoning in the body is right), and the test suite covers requested-locale hit, plain text, missing locale, empty locale, empty default, encode filtering, and a round-trip. no code asks from me.

gate: branch is behind main; rebase and rerun CI, then this is good to merge. (independent of your #1023/#1024, no stacking.)

[sshdopey]

Auto-review failed (API error). Leaving PR for human review.

[davidmaronio]

rebase looks good and the pr is still tightly scoped to the util and its tests. merging.