Add `next-intl` locale coverage for `fr-CA`, `pt-BR`, `sw` (Swahili)

[kilodesodiq-arch]

Problem Statement. app/frontend/src/i18n.ts declares ['en', 'es', 'fr']. Crisis
response contexts are FR/PT/Swahili-dominant.

Technical Context. app/frontend/src/i18n.ts,
app/frontend/src/messages/*.

Expected Outcome. New translation files for fr-CA, pt-BR, sw.

Acceptance Criteria.

• pnpm dev shows the locale switcher for each.
• A e2e test asserts /fr-CA/dashboard renders without missing-key warnings.

Files or modules likely to be affected.
src/i18n.ts,
new src/messages/{fr-CA,pt-BR,sw}.json.

Difficulty. Easy
Estimated effort. M

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Backlog item #83 from `docs/maintainer-issue-backlog.md.

[abimbolaalabi]

Hi Maintainer! I’m interested in contributing to this task and can ensure timely delivery with clean implementation. I’ve thoroughly read the issue description and understand the expected outcome. I’d love to work on it. Thank You!

[grantfox-oss]

🦊 GrantFox — @abimbolaalabi has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #291)
2. Your PR will be reviewed by the ChainForgee maintainers

Good luck! Track your progress on GrantFox.