feat: LLM entity + fact extraction pipeline (Zep paper alignment) (#48)

## Changes

### Entity Extraction
- Switch from WikiLinkFallbackExtractor to LlmEntityExtractor when LLM_ENDPOINT set
- `clean_llm_response()`: strips `<think>` tags, markdown fences, extracts JSON
- Handle array responses (Ollama returns `[...]` not `{entities: [...]}`)
- EntityType custom Deserialize: unknown variants → Unknown (no crash)
- Increase timeout 30s→90s, max_tokens 500→1500 for reasoning models
- Graceful reflection fallback: keep entities if verification fails

### Fact Extraction (NEW)
- LlmFactExtractor: LLM-based relationship extraction between entity pairs
- Validates source/target against known entity list (drops hallucinated edges)
- Same robust JSON cleaning for reasoning models + Ollama
- IngestWorker auto-selects LLM vs Simple based on LLM_ENDPOINT env

### K8s Deployment
- Add `command: ["/app/mem"]` (fix args replacing CMD)
- Add LLM_ENDPOINT, LLM_MODEL env vars for in-cluster LLM

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

## Zep Paper Alignment (§2.2)
- Entity extraction + resolution (§2.2.1)
- Fact extraction between entity pairs (§2.2.2)
- Temporal edge invalidation ready (t_valid/t_invalid schema)
- Reflection verification (§2.2.1, graceful fallback)

---------

Co-authored-by: rock <[email protected]>
Reviewed-on: #48
Co-authored-by: poimen <[email protected]>

crates/mem-cli/src/chunk_optimizer.rs

@@ -211,17 +211,32 @@ impl ChunkOptimizer {
 
     /// End-to-end optimization pipeline
     pub fn optimize(&self, chunks: Vec<OptimizableChunk>) -> (Vec<OptimizableChunk>, SelectionMetrics) {
+        let input_count = chunks.len();
+
         // Step 1: Filter by threshold
         let filtered = self.threshold_filter.filter(chunks.clone());
+        let after_filter = filtered.len();
 
         // Step 2: Deduplicate
         let (deduplicated, dedup_removed) = self.deduplicator.deduplicate(filtered);
+        let after_dedup = deduplicated.len();
 
         // Step 3: Select within budget
         let (selected, mut metrics) = self.budget_selector.select(deduplicated);
-
         metrics.dedup_removed = dedup_removed;
 
+        tracing::info!(
+            target: "observability",
+            event = "chunk_optimize",
+            input = input_count,
+            after_threshold_filter = after_filter,
+            after_dedup = after_dedup,
+            dedup_removed = dedup_removed,
+            selected = selected.len(),
+            budget_bytes = metrics.total_bytes,
+            "Chunk optimization complete"
+        );
+
         (selected, metrics)
     }
 }