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/test_client_tools.py

@@ -8,8 +8,8 @@ from unittest.mock import Mock
 
 import pytest
 
-from application.agents.tool_executor import ToolExecutor
-from application.llm.handlers.base import LLMHandler, LLMResponse, ToolCall
+from docsgpt.agents.tool_executor import ToolExecutor
+from docsgpt.llm.handlers.base import LLMHandler, LLMResponse, ToolCall
 
 
 # ---------------------------------------------------------------------------
@@ -205,7 +205,7 @@ class TestGetToolsAutoMerge:
         mock_db = MagicMock()
         mock_db.__getitem__.return_value.find.return_value = iter([])
         monkeypatch.setattr(
-            "application.agents.tool_executor.MongoDB.get_client",
+            "docsgpt.agents.tool_executor.MongoDB.get_client",
             lambda: mock_db,
         )
         executor = ToolExecutor(user="alice")
@@ -227,7 +227,7 @@ class TestGetToolsAutoMerge:
         mock_db = MagicMock()
         mock_db.__getitem__.return_value.find.return_value = iter([])
         monkeypatch.setattr(
-            "application.agents.tool_executor.MongoDB.get_client",
+            "docsgpt.agents.tool_executor.MongoDB.get_client",
             lambda: mock_db,
         )
         executor = ToolExecutor(user="alice")