chore: merge upstream/main into the fork

[fabolivark]

What

Merges upstream/main (croffasia/itsaplan, 8 commits since 1a743218) into the fork.

Upstream squash-merged the fork's Plane import/export work as croffasia#389 and then built on
top of it (croffasia#419 subtask progress, croffasia#420 tabbed import/export with a source picker), so
that code arrives from both sides. All 13 conflicts sit in that shared area.

Conflicts resolved:

File	Resolution
docker-compose.coolify.yml	ours — the configurable S3_ENDPOINT / S3_ACCESS_KEY_ID defaults stay
apps/api/src/modules/settings/service.ts	both — the Locale import alongside upstream's comment
import-export/*.tsx, 9 × messages/*/settings.json	upstream — it only adds the new import / source / sourceHint / comingSoon keys over the already-squashed contribution

The only files removed relative to the fork's main are docs/pr-screenshots/*.png,
upstream's own cleanup in croffasia#418. Instance branding, the god overrides, the external S3
setting and the es-ES translations are all unchanged.

Why

Keep the fork current with upstream without losing the instance customisations.

How to test

bun install
bun run typecheck && bun run lint && bun run format:check
docker compose -f docker-compose.test.yml build
docker compose -f docker-compose.test.yml run --rm api-test

Merge this with a merge commit, not a squash. Squashing discards the merge
lineage, so the next upstream sync would re-resolve every one of these conflicts.

Checklist

• bun run typecheck passes
• bun run lint and bun run format:check pass
• Tests added or updated for the changed behaviour — test gate passes: 1947 + 4 + 79 tests, 0 failures
• Database schema changed: migration generated with bun run db:generate and committed — no schema change beyond what upstream already carries
• New environment variables documented in .env.example
• Docs updated (README.md or the relevant AGENTS.md)

Screenshots

Upstream's croffasia#420 changes the Import/Export settings page (two tabs and a source
picker). I did not look at the merged UI — no screenshots were taken of it.