feat(ai-services): add Python FastAPI AI/ML services container

Create libs/ai-services/ with FastAPI app providing:
- POST /avm/predict — XGBoost-backed property price prediction (heuristic fallback)
- POST /avm/extract-features — Vietnamese NLP feature extraction from listing text
- POST /moderation/check — content moderation with rule-based flagging
- GET /health — health check endpoint

Includes Dockerfile (Python 3.12), docker-compose integration, Pydantic models,
and 9 passing tests covering all endpoints.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

libs/ai-services/app/services/moderation_service.py

@@ -0,0 +1,96 @@
+import re
+
+from app.models.moderation import ModerationFlag, ModerationRequest, ModerationResponse
+
+# Blocklist categories with patterns and severity
+_RULES: list[dict] = [
+    {
+        "category": "contact_info",
+        "severity": "medium",
+        "patterns": [
+            re.compile(r"0\d{9,10}"),  # Vietnamese phone numbers
+            re.compile(r"\b[\w.+-]+@[\w-]+\.[\w.]+\b"),  # Email
+            re.compile(r"(?:zalo|viber|telegram|whatsapp)\s*[:\-]?\s*\d+", re.IGNORECASE),
+        ],
+        "reason": "Contact information detected — may bypass platform messaging",
+    },
+    {
+        "category": "spam",
+        "severity": "low",
+        "patterns": [
+            re.compile(r"(.)\1{5,}"),  # Repeated characters
+            re.compile(r"(!!!|\.\.\.){3,}"),  # Excessive punctuation
+            re.compile(r"(?:click|nhấn|bấm)\s+(?:here|vào đây|link)", re.IGNORECASE),
+        ],
+        "reason": "Spam-like content pattern",
+    },
+    {
+        "category": "profanity",
+        "severity": "high",
+        "patterns": [
+            re.compile(
+                r"\b(?:lừa đảo|scam|fake|giả mạo)\b",
+                re.IGNORECASE,
+            ),
+        ],
+        "reason": "Potentially harmful or fraudulent language",
+    },
+    {
+        "category": "prohibited_content",
+        "severity": "high",
+        "patterns": [
+            re.compile(
+                r"\b(?:đất rừng phòng hộ|đất quốc phòng|đất tranh chấp)\b",
+                re.IGNORECASE,
+            ),
+        ],
+        "reason": "Listing references prohibited property types",
+    },
+]
+
+
+class ModerationService:
+    def check(self, req: ModerationRequest) -> ModerationResponse:
+        flags: list[ModerationFlag] = []
+        text = req.text
+
+        for rule in _RULES:
+            for pattern in rule["patterns"]:
+                for match in pattern.finditer(text):
+                    flags.append(
+                        ModerationFlag(
+                            category=rule["category"],
+                            severity=rule["severity"],
+                            matched_text=match.group(),
+                            reason=rule["reason"],
+                        )
+                    )
+
+        if not flags:
+            return ModerationResponse(
+                is_flagged=False,
+                score=0.0,
+                flags=[],
+                cleaned_text=text,
+            )
+
+        # Compute aggregate score
+        severity_weights = {"low": 0.2, "medium": 0.5, "high": 0.9}
+        max_score = max(severity_weights.get(f.severity, 0.5) for f in flags)
+        avg_score = sum(severity_weights.get(f.severity, 0.5) for f in flags) / len(flags)
+        score = round(min(1.0, max_score * 0.7 + avg_score * 0.3), 3)
+
+        # Redact flagged content
+        cleaned = text
+        for flag in flags:
+            cleaned = cleaned.replace(flag.matched_text, "[REDACTED]")
+
+        return ModerationResponse(
+            is_flagged=True,
+            score=score,
+            flags=flags,
+            cleaned_text=cleaned,
+        )
+
+
+moderation_service = ModerationService()