chore: [DHIS2-21969] Refine custom terminology label support

[henrikmv]

DHIS2-21969

This PR replaces the multi-function custom terminology API (getProgramLabel, getStageLabel, useProgramLabel, useStageLabel, useTrackedEntityTypeLabel) with a unified two-function API:

// Non-hook (usable anywhere)
getTermLabel(key, { programId, stageId?, plural? })

// React hook (reads programId from Redux)
useTermLabel(key, { programId?, stageId?, plural? })

Additional changes:

• withCustomLabels HOC — injects resolved terminology labels as props
• i18n interpolator patch — auto-capitalizes leading custom-term variables and disables HTML escaping for them
• Feature-gated plural fields — plural terminology fields are only requested from backend ≥ v43

[github-actions]

🚀 Deployed on https://deploy-preview-4728.capture.netlify.dhis2.org

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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