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/full_pipeline.rs

@@ -344,6 +344,22 @@ impl FullPipeline {
 
         metrics.total_latency_ms = start.elapsed().as_millis() as u64;
 
+        tracing::info!(
+            target: "observability",
+            event = "full_pipeline_complete",
+            query = query,
+            candidates = metrics.wiki_scope_docs,
+            prefiltered = metrics.prefilter_candidates,
+            optimized = metrics.post_optimization_count,
+            dedup_removed = metrics.dedup_removed,
+            boosts_applied = metrics.metadata_boosts_applied,
+            cache_hit_ratio = format!("{:.2}", metrics.cache_hit_ratio),
+            budget_bytes = metrics.budget_used_bytes,
+            total_ms = metrics.total_latency_ms,
+            "Full query pipeline complete"
+        );
+
+
         Ok(PipelineResult {
             query: query.to_string(),
             query_intent,
@@ -467,6 +483,22 @@ impl FullPipeline {
 
         metrics.total_latency_ms = start.elapsed().as_millis() as u64;
 
+        tracing::info!(
+            target: "observability",
+            event = "full_pipeline_complete",
+            query = query,
+            candidates = metrics.wiki_scope_docs,
+            prefiltered = metrics.prefilter_candidates,
+            optimized = metrics.post_optimization_count,
+            dedup_removed = metrics.dedup_removed,
+            boosts_applied = metrics.metadata_boosts_applied,
+            cache_hit_ratio = format!("{:.2}", metrics.cache_hit_ratio),
+            budget_bytes = metrics.budget_used_bytes,
+            total_ms = metrics.total_latency_ms,
+            "Full query pipeline complete"
+        );
+
+
         Ok(PipelineResult {
             query: query.to_string(),
             query_intent,