librarian: mount + seed runtime JSON state under /lib_temp_files

(Re-applied cleanly on top of main: PR #18 was rebase-merged, so the branch
that became #19 conflicted on the already-landed commits. This carries ONLY
the librarian state fix - the sole content difference between that branch
and main - so nothing else is touched or lost.)

The worker threads open cr_results/rr_results/not_in_db/s_results.json in
place ('r+'), crashing with FileNotFoundError in a fresh container. New
conjurer_librarian/lib_paths.py resolves all four under a persistent dir
(CONJURER_LIBRARIAN_STATE_DIR, default /lib_temp_files) and seeds missing
ones with '{}' on import; shared by conjurer_librarian.py and scrape_bot.py
(no circular import). ndb_database/database initialised to {} before load so
a corrupt persisted file degrades to empty instead of NameError. search_bot
/search_bot2 open the DOI DB 'r' not 'r+' so /doi can stay read-only. Docker:
STATE_DIR env + VOLUME, compose mounts /srv/librarian/state:/lib_temp_files.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

conjurer_librarian/conjurer_librarian.py

@@ -25,6 +25,7 @@ from queue import Queue
 from typing import Dict, Optional
 
 import requests
+import lib_paths
 import scrape_bot
 import search_bot
 # import search_bot2 as search_bot
@@ -194,7 +195,7 @@ class Librarian(object):
             self.app.logger.info("CROSSREF DONE")
 
             self.app.logger.info("CROSSREF DONE")
-        with open("cr_results.json", "r+", encoding="utf-8") as data_file:
+        with open(lib_paths.CR_RESULTS, "r+", encoding="utf-8") as data_file:
             # First we load existing data into a dict.
             try:
                 file_data = json.load(data_file)
@@ -258,7 +259,7 @@ class Librarian(object):
 
         for item in temp:
             refined_result[item["DOI"]]=  item
-        with open("rr_results.json", "r+", encoding="utf-8") as data_file:
+        with open(lib_paths.RR_RESULTS, "r+", encoding="utf-8") as data_file:
             # First we load existing data into a dict.
             try:
                 file_data = json.load(data_file)
@@ -417,7 +418,8 @@ class BackgroundTaskSearch(threading.Thread):
             self.app.logger.info("Saving to file")
 
             # Save results to "not_in_db.json" file
-            with open("not_in_db.json", "r+", encoding="utf-8") as ndb_file:
+            with open(lib_paths.NOT_IN_DB, "r+", encoding="utf-8") as ndb_file:
+                ndb_database = {}
                 try:
                     ndb_database = json.load(ndb_file)
                 except JSONDecodeError:
@@ -431,7 +433,8 @@ class BackgroundTaskSearch(threading.Thread):
                 json.dump(ndb_database, ndb_file)
 
             # Save results to "s_results.json" file
-            with open("s_results.json", "r+", encoding="utf-8") as s_file:
+            with open(lib_paths.S_RESULTS, "r+", encoding="utf-8") as s_file:
+                database = {}
                 try:
                     database = json.load(s_file)
                 except JSONDecodeError: