refactor: rename the application package to docsgpt

The backend import package is now docsgpt, the name it will carry on PyPI;
application was far too generic to install into anyone's site-packages.
git mv plus a mechanical rewrite of every import, dotted string and path
reference: 734 Python files, the compose files, Dockerfile, workflows, docs,
setup scripts, devcontainer, k8s manifests, vscode config, pytest and coverage
config, .gitignore. Behaviour is unchanged.

Kept for one release:
- A top-level application package whose meta-path finder resolves
  application.x.y to the already-imported docsgpt.x.y object, so old imports
  and entry points (celery -A application.app.celery,
  uvicorn application.asgi:asgi_app) keep working with a FutureWarning.
- Celery registers every application.* task name as an alias of its
  docsgpt.* task on start-up, so messages queued by the previous release still
  run. The redbeat key prefix moves to redbeat:docsgpt:v2: so schedule entries
  the previous release wrote are left unread instead of firing twice.

The backend image builds from the repository root (docker build -f
docsgpt/Dockerfile .) so it can ship the alias package; a root .dockerignore
allow-lists docsgpt/ and application/ and keeps caches, local data, .env
files, the sample index files and the Dockerfile out. Compose and the image
workflows point at the new context.

tests/parser/connectors/confluence/test_auth_session.py

@@ -13,14 +13,14 @@ def _patch_db(conn):
         yield conn
 
     with patch(
-        "application.storage.db.session.db_readonly", _yield
+        "docsgpt.storage.db.session.db_readonly", _yield
     ):
         yield
 
 
 class TestGetTokenInfoFromSession:
     def test_invalid_session_token_raises(self, pg_conn):
-        from application.parser.connectors.confluence.auth import (
+        from docsgpt.parser.connectors.confluence.auth import (
             ConfluenceAuth,
         )
 
@@ -29,10 +29,10 @@ class TestGetTokenInfoFromSession:
             auth.get_token_info_from_session("no-such-token")
 
     def test_missing_token_info_raises(self, pg_conn):
-        from application.parser.connectors.confluence.auth import (
+        from docsgpt.parser.connectors.confluence.auth import (
             ConfluenceAuth,
         )
-        from application.storage.db.repositories.connector_sessions import (
+        from docsgpt.storage.db.repositories.connector_sessions import (
             ConnectorSessionsRepository,
         )
 
@@ -47,10 +47,10 @@ class TestGetTokenInfoFromSession:
             auth.get_token_info_from_session("tok-no-info")
 
     def test_missing_required_fields_raises(self, pg_conn):
-        from application.parser.connectors.confluence.auth import (
+        from docsgpt.parser.connectors.confluence.auth import (
             ConfluenceAuth,
         )
-        from application.storage.db.repositories.connector_sessions import (
+        from docsgpt.storage.db.repositories.connector_sessions import (
             ConnectorSessionsRepository,
         )
 
@@ -70,10 +70,10 @@ class TestGetTokenInfoFromSession:
             auth.get_token_info_from_session("tok-partial")
 
     def test_complete_token_info_returned(self, pg_conn):
-        from application.parser.connectors.confluence.auth import (
+        from docsgpt.parser.connectors.confluence.auth import (
             ConfluenceAuth,
         )
-        from application.storage.db.repositories.connector_sessions import (
+        from docsgpt.storage.db.repositories.connector_sessions import (
             ConnectorSessionsRepository,
         )