Revert "refactor: clean up legacy code, rename hopper to entity_extractor, and add third-party notices"

This reverts commit 54fcef9887.

Please do not submit unrelated docs and codes in the same commit. I am reverting this commit so that the related files can be submitted in better-organized future commits.

artemis/resources/config/artemis.jsonc

@@ -93,8 +93,8 @@
     // 📋 Summarizer: Aggregates step history and generates structured outcome
     "summarizer": {},
 
-    // 🔍 Entity Extractor: Fast lightweight package name locator and entity extractor
-    "entity_extractor": {
+    // 🔽 Hopper: Fast lightweight package name locator
+    "hopper": {
       "model": "gemini-3.5-flash-lite",
       "fallback": {
         "provider": "google",