feat: LLM-based fact extraction + robust entity parsing

Entity extraction fixes:
- clean_llm_response() strips <think> tags, markdown fences, extracts JSON
- Handle array responses (wrap in {"entities": [...]})
- EntityType custom Deserialize: unknown variants map to Unknown (not crash)
- Increase timeout to 90s for reasoning models
- Increase max_tokens to 1500 for reasoning model overhead

Fact extraction (new):
- LlmFactExtractor: LLM-based relationship extraction between entities
- Validates source/target against known entity list (no hallucinated edges)
- Same clean_llm_response() for reasoning model + Ollama compatibility
- Graceful fallback: returns empty on LLM error (no pipeline crash)
- IngestWorker uses LlmFactExtractor when LLM_ENDPOINT set

K8s deployment:
- Add LLM_ENDPOINT, LLM_API_BASE, LLM_MODEL env vars
- Points to in-cluster reasoning-predictor service

Tested E2E with local Ollama (qwen2.5:3b):
- 12 entities extracted (person, tool, concept, organization)
- 5 edges with meaningful relationships and facts
- 781 tests pass

crates/mem-core/src/entity.rs

@@ -8,7 +8,7 @@ use time::OffsetDateTime;
 use std::fmt;
 
 /// Entity type classification (extensible enum).
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Hash)]
 #[serde(rename_all = "snake_case")]
 pub enum EntityType {
     Person,
@@ -59,6 +59,16 @@ impl EntityType {
     }
 }
 
+impl<'de> serde::Deserialize<'de> for EntityType {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let s = String::deserialize(deserializer)?;
+        Ok(Self::from_str(&s))
+    }
+}
+
 impl fmt::Display for EntityType {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{}", self.as_str())