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/test_workflow_portability.py

@@ -1,4 +1,4 @@
-"""Workflow-agent YAML export/import (application.api.user.agents.portability).
+"""Workflow-agent YAML export/import (docsgpt.api.user.agents.portability).
 
 Real SQL against the ephemeral ``pg_conn`` fixture, like
 ``test_agent_portability.py``. Covers the graph block: reference rewriting
@@ -11,8 +11,8 @@ from __future__ import annotations
 
 import pytest
 
-from application.agents.default_tools import default_tool_id
-from application.api.user.agents.portability import (
+from docsgpt.agents.default_tools import default_tool_id
+from docsgpt.api.user.agents.portability import (
     AgentImportError,
     agent_to_yaml,
     apply_import,
@@ -20,15 +20,15 @@ from application.api.user.agents.portability import (
     plan_import,
     serialize_agent,
 )
-from application.storage.db.repositories.agents import AgentsRepository
-from application.storage.db.repositories.sources import SourcesRepository
-from application.storage.db.repositories.user_custom_models import (
+from docsgpt.storage.db.repositories.agents import AgentsRepository
+from docsgpt.storage.db.repositories.sources import SourcesRepository
+from docsgpt.storage.db.repositories.user_custom_models import (
     UserCustomModelsRepository,
 )
-from application.storage.db.repositories.user_tools import UserToolsRepository
-from application.storage.db.repositories.workflow_edges import WorkflowEdgesRepository
-from application.storage.db.repositories.workflow_nodes import WorkflowNodesRepository
-from application.storage.db.repositories.workflows import WorkflowsRepository
+from docsgpt.storage.db.repositories.user_tools import UserToolsRepository
+from docsgpt.storage.db.repositories.workflow_edges import WorkflowEdgesRepository
+from docsgpt.storage.db.repositories.workflow_nodes import WorkflowNodesRepository
+from docsgpt.storage.db.repositories.workflows import WorkflowsRepository
 
 
 pytestmark = pytest.mark.integration
@@ -325,7 +325,7 @@ def test_import_route_rejects_invalid_graph_as_client_error(pg_conn):
 
     from flask import Flask, request
 
-    from application.api.user.agents.portability import ImportAgent
+    from docsgpt.api.user.agents.portability import ImportAgent
 
     @contextmanager
     def _conn():
@@ -345,7 +345,7 @@ def test_import_route_rejects_invalid_graph_as_client_error(pg_conn):
     )
     app = Flask(__name__)
     with patch(
-        "application.api.user.agents.portability.db_session", _conn
+        "docsgpt.api.user.agents.portability.db_session", _conn
     ), app.test_request_context(
         "/api/import_agent", method="POST", json={"yaml": yaml_text}
     ):