feat: add 5 deterministic rules (IMU outliers/watchdog, USBL SNR/spike, battery_low)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/cosma_log_analyzer/rules/base.py

@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+
+import pandas as pd
+
+from ..models import Anomaly
+
+
+class Rule(ABC):
+    """Base class for detection rules.
+
+    Subclasses declare class attributes `name`, `topic`, `severity`, then
+    implement `detect(df)` which receives the topic-specific DataFrame and
+    returns a list of Anomaly instances.
+    """
+
+    name: str = "rule"
+    topic: str = ""
+    severity: str = "warn"
+
+    def __init__(self, subject: str = "AUV000") -> None:
+        self.subject = subject
+
+    def bind(self, subject: str) -> "Rule":
+        self.subject = subject
+        return self
+
+    @abstractmethod
+    def detect(self, df: pd.DataFrame) -> list[Anomaly]:
+        ...
+
+    def _make(
+        self,
+        ts: float,
+        value: float | None,
+        context: dict,
+    ) -> Anomaly:
+        return Anomaly(
+            rule=self.name,
+            severity=self.severity,
+            timestamp=float(ts),
+            subject=self.subject,
+            topic=self.topic,
+            value=value,
+            context=context,
+        )