Fix Combined language hierarchy for ISO-only groupings

[whwan4570]

Summary

Rebased on latest master and addresses @conradarcturus review on #651.

• Replace reparent-children-except with explicit row-per-child entries in languageFamilyCombinedOverrides.tsv
• Add Formosan children under fox, plus Conrad's additional ISO-only groupings (sdv, omv, sai, ssa, nic)
• Apply overrides after Glottolog load; only Combined.parentLanguageCode is modified

Fixes #650

Supersedes #651 and #684 (same change set, now on upstream branch for deploy-preview).

Test plan

• npm run test:run — CombinedFamilyOverrides.test.ts
• npm run lint && npm run build
• Hierarchy UI verified locally (Combined source) — see PR comment with screenshots

Made with Cursor

[whwan4570]

@conradarcturus Re-review requested — same code as #684, now on upstream branch so deploy-preview should pass.

Hierarchy verification (Combined source, local dev)

Base: http://localhost:5174/lang-nav/data?view=Hierarchy&languageSource=Combined&languageScopes=5,4,3,2

Group	URL
Formosan (fox)	open
Albanian	open
Quechuan	open
Basque	open
Nilotic (sdv)	open
Omotic (omv)	open
South American Indian (sai)	open
Nilo-Saharan (ssa)	open
Dogon (nic)	open

Screenshots captured locally (same set as #651 review): docs/pr-651-screenshots/ — 9 PNGs.

[github-actions]

Cloudflare Pages preview

• Deploy URL: https://97ab8851.lang-nav.pages.dev/lang-nav/
• Branch alias: https://pr-685.lang-nav.pages.dev/lang-nav/
  Commit: 9467361

[whwan4570]

Hierarchy screenshots (Combined source)

Local verification — same views as #651 review:

1. Formosan (fox)
2. Albanian
3. Quechuan
4. Basque
5. Nilotic (sdv)
6. Omotic (omv)
7. South American Indian (sai)
8. Nilo-Saharan (ssa)
9. Dogon (nic)

[conradarcturus]

Thanks for making the updates from #651

This looks great! I'm not sure why cloudflare is having issues -- but you can go ahead and merge this PR.