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/api/user/test_tools_artifact_generalized.py

@@ -8,10 +8,10 @@ from contextlib import contextmanager
 import pytest
 from flask import request
 
-from application.storage.db.repositories.artifacts import ArtifactsRepository
-from application.storage.db.repositories.conversations import ConversationsRepository
-from application.storage.db.repositories.notes import NotesRepository
-from application.storage.db.repositories.user_tools import UserToolsRepository
+from docsgpt.storage.db.repositories.artifacts import ArtifactsRepository
+from docsgpt.storage.db.repositories.conversations import ConversationsRepository
+from docsgpt.storage.db.repositories.notes import NotesRepository
+from docsgpt.storage.db.repositories.user_tools import UserToolsRepository
 
 
 @pytest.fixture
@@ -22,13 +22,13 @@ def _patch_db(pg_conn, monkeypatch):
     def _use_conn():
         yield pg_conn
 
-    monkeypatch.setattr("application.api.user.tools.routes.db_readonly", _use_conn)
-    monkeypatch.setattr("application.api.user.artifacts.routes.db_readonly", _use_conn)
+    monkeypatch.setattr("docsgpt.api.user.tools.routes.db_readonly", _use_conn)
+    monkeypatch.setattr("docsgpt.api.user.artifacts.routes.db_readonly", _use_conn)
     return pg_conn
 
 
 def _get(flask_app, artifact_id, token):
-    from application.api.user.tools.routes import GetArtifact
+    from docsgpt.api.user.tools.routes import GetArtifact
 
     with flask_app.app_context():
         with flask_app.test_request_context():