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/agents/test_telegram_tool.py

@@ -1,10 +1,10 @@
-"""Tests for application/agents/tools/telegram.py"""
+"""Tests for docsgpt/agents/tools/telegram.py"""
 
 from unittest.mock import MagicMock, patch
 
 import pytest
 
-from application.agents.tools.telegram import TelegramTool
+from docsgpt.agents.tools.telegram import TelegramTool
 
 
 @pytest.fixture
@@ -18,7 +18,7 @@ class TestTelegramExecuteAction:
         with pytest.raises(ValueError, match="Unknown action"):
             tool.execute_action("invalid")
 
-    @patch("application.agents.tools.telegram.requests.post")
+    @patch("docsgpt.agents.tools.telegram.requests.post")
     def test_send_message(self, mock_post, tool):
         mock_resp = MagicMock()
         mock_resp.status_code = 200
@@ -35,7 +35,7 @@ class TestTelegramExecuteAction:
         assert call_args[1]["data"]["text"] == "Hello"
         assert call_args[1]["data"]["chat_id"] == "12345"
 
-    @patch("application.agents.tools.telegram.requests.post")
+    @patch("docsgpt.agents.tools.telegram.requests.post")
     def test_send_image(self, mock_post, tool):
         mock_resp = MagicMock()
         mock_resp.status_code = 200
@@ -51,7 +51,7 @@ class TestTelegramExecuteAction:
         assert "bot123:ABC/sendPhoto" in call_args[0][0]
         assert call_args[1]["data"]["photo"] == "https://img.com/cat.jpg"
 
-    @patch("application.agents.tools.telegram.requests.post")
+    @patch("docsgpt.agents.tools.telegram.requests.post")
     def test_api_error_status(self, mock_post, tool):
         mock_resp = MagicMock()
         mock_resp.status_code = 403