chore(core): freeze shared core contracts — ScrubbedText, RiskLevel, AlertLevel, privacy signatures

Lets #2-#7 proceed in parallel against stable interfaces.

Refs #2

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/core/privacy.py

@@ -0,0 +1,13 @@
+"""PII scrubbing and pseudonymisation (issue #2). Contract stub — implementation lands in #2."""
+
+from app.core.types import ScrubbedText
+
+
+def scrub(text: str) -> ScrubbedText:
+    """Replace personal data (phones, emails, SNILS, names, addresses...) with placeholders."""
+    raise NotImplementedError
+
+
+def pseudo_id(snils: str, key: str | None = None) -> str:
+    """HMAC-SHA256(PSEUDO_KEY, normalised SNILS) as 32 hex chars — the token linking identity and clinical DBs."""
+    raise NotImplementedError