perf: build info log messages lazily so raising the log level actually saves work (#27837)

Raising GLOBAL_LOG_LEVEL to WARNING buys quieter output but not less work: 241 INFO call sites interpolate their payload into an f-string before the logging call gets to drop it. The heaviest is get_doc, which logs every chunk id and metadata dict in a collection, so on the full-context retrieval path that is the entire knowledge base, once per chat request.

That one line at WARNING, CPython 3.12:

| knowledge base | payload | before   | after   |
| -------------- | ------- | -------- | ------- |
| top-k of 3     | 1.2 kB  | 3.8 us   | 0.07 us |
| 500 chunks     | 201 kB  | 583.6 us | 0.08 us |
| 5000 chunks    | 2.0 MB  | 5.8 ms   | 0.15 us |

The lazy form log.info('query_doc:result %s %s', result.ids, result.metadatas) hands the payload to record.getMessage(), which the InterceptHandler only reaches once a record has passed the level check. Output at INFO is byte-identical. Two sites that already built their message eagerly, one str concat and one % operator, move to the same lazy form.

backend/open_webui/utils/auth.py

@@ -542,7 +542,7 @@ async def create_admin_user(email: str, password: str, name: str = 'Admin'):
         log.debug('Users already exist, skipping admin creation')
         return None
 
-    log.info(f'Creating admin account from environment variables: {email}')
+    log.info('Creating admin account from environment variables: %s', email)
     try:
         hashed = await get_password_hash(password)
         user = await Auths.insert_new_auth(
@@ -552,7 +552,7 @@ async def create_admin_user(email: str, password: str, name: str = 'Admin'):
             role='admin',
         )
         if user:
-            log.info(f'Admin account created successfully: {email}')
+            log.info('Admin account created successfully: %s', email)
             return user
         else:
             log.error('Failed to create admin account from environment variables')