Add DeLTA, FeatureRecord, and harmonisation checks to CI

[yuqiliang]

What changed

The Validate data packages workflow previously ran the MOSAIQ linkage check (validate_mosaiq.py) for ISD, ARAUS, and SATP only, and never ran two other validators that already exist in the repo. This extends CI so every built package and validator is exercised on push and PR:

• DeLTA added to the existing MOSAIQ linkage step (validate_mosaiq.py --skip-file-check)
• New step Check FeatureRecords — runs check_feature_records.py for ISD / ARAUS / SATP (DeLTA has no features.csv, and the script only accepts those three)
• New step Validate schema-level harmonisation — runs validate_schema_harmonisation.py

Why

DeLTA and the two Python validators all pass locally but were not protected by CI, so a regression in any of them could land on main unnoticed.

Verification

Every new step was run locally before being wired in:

Step	Result
validate_mosaiq.py DeLTA	pass (2,890 clips)
check_feature_records.py ISD / ARAUS / SATP	PASS (4 / 2 / 1 feature rows)
validate_schema_harmonisation.py	0 errors, 0 warnings

validate.yml parses as valid YAML (12 steps).

Notes for reviewer

• Scope is intentionally limited to .github/workflows/validate.yml (1 file changed, 17 insertions, 1 deletion).
• The other in-flight working-tree changes (SATP ratings/preprocessing/features, new feature scripts, shared schemas) are deliberately excluded from this PR.

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