feat: add Croatian (hr) PII language pack with OIB validator

[PouyanJay]

Summary

Implements #889: adds Croatian as a national-ID-only language pack, mirroring the structure of the Latvian pack and the sibling packs proposed in #1592 (Estonian) and #1597 (Serbian).

• validate_croatian_oib: 11-digit OIB with an ISO 7064 MOD 11,10 check digit over the first 10 digits; OIB has no embedded structure, so validation is checksum + shape
• _CROATIAN_PII_PATTERNS: OIB national_id plus Croatian date, phone (+385), street-address (ulica/trg/avenija/cesta), and context-gated postcode cues
• hr registered in LANGUAGE_PII_PATTERNS / NATIONAL_ID_ONLY_LANGUAGES, hr -> hr_HR locale (native Faker locale), fake data, locale format hints
• Synthetic golden fixture at openmed/eval/golden/fixtures/i18n/hr.jsonl (the issue's golden/hr.jsonl path is not read by the fixture loader; all sibling fixtures live under fixtures/i18n/)

No custom Faker provider (deviation from the issue's letter)

The issue asks for "an OIB Faker surrogate provider", but Faker's native hr_HR.ssn() already generates ISO 7064-valid OIBs — verified 500/500 samples against this PR's independently implemented validator, plus a 200-sample seeded round-trip in the test suite. It is therefore registered with faker_method="ssn" through the national-ID registry, exactly like the existing Turkish TCKN registration, with no custom provider class. This keeps clinical_ids.py and providers/__init__.py untouched and the diff at 7 files.

Relationship to #1592 and #1597

The three PII-pack PRs add adjacent lines to the same registries (NATIONAL_ID_ONLY_LANGUAGES, LANG_TO_LOCALE, NATIONAL_ID_PROVIDERS, _LOCALE_ID_METHODS, and the exact-set test assertion). They are independent and mergeable in any order; whichever PRs merge later will be rebased promptly (mechanical one-line conflicts only).

Data provenance

Every OIB in code, tests, and the fixture is synthetic, generated algorithmically from the ISO 7064 rules. No real personal identifiers anywhere.

Verification

• make test: 4680 passed, 44 skipped, 0 failed
• pre-commit hooks pass on all changed files
• Locale-coherence gate auto-covers hr, including a 40-seed surrogate -> validator round-trip
• Golden fixture de-identifies offline with zero leakage

Out of scope, as per the issue: no Croatian model training, no registry data bundled.

Closes #889

[maziyarpanahi]

Pouyan, thank you for this polished Croatian language pack. The ISO 7064 OIB validator, native Faker integration, synthetic golden fixture, registry wiring, and no-leakage coverage fit the existing architecture very well.

I verified the OIB algorithm against Croatia’s official specification and added a focused maintainer hardening pass: canonical 11 ASCII digits are now required without silent trimming or normalization, and the digit-only safety sweep remains context-gated to avoid broad false positives. Your original commit is preserved and the branch is current with master. The focused coverage passes, the full suite passes (4,801 tests, 52 skipped), formatting, lint, and type gates pass, and all hosted checks are green. This is ready to merge—thank you for the consistently thoughtful work.