feat: observability logs across entire query + compaction pipeline

All components now emit target="observability" structured logs:

chunk_optimizer:
  event=chunk_optimize: input, after_threshold_filter, after_dedup,
    dedup_removed, selected, budget_bytes

result_compressor:
  event=result_compress: input_count, estimated_bytes, compressed_bytes,
    budget_bytes, strategy

query_router:
  event=query_route: route, candidates, prefiltered, selected, latency_ms

cache_alignment:
  event=cache_preload: preloaded, cache_hits, cache_misses, hit_ratio

full_pipeline:
  event=full_pipeline_complete: query, candidates, prefiltered, optimized,
    dedup_removed, boosts_applied, cache_hit_ratio, budget_bytes, total_ms

compaction:
  event=compaction_complete: mode, duration_ms, duplicate_edges_deleted,
    stale_facts_deleted, semantic_merged, llm_calls, bytes_freed

781 tests pass.

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)
     }
 }