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_postgres_tool.py

@@ -1,10 +1,10 @@
-"""Tests for application/agents/tools/postgres.py"""
+"""Tests for docsgpt/agents/tools/postgres.py"""
 
 from unittest.mock import MagicMock, patch
 
 import pytest
 
-from application.agents.tools.postgres import PostgresTool
+from docsgpt.agents.tools.postgres import PostgresTool
 
 
 @pytest.fixture
@@ -18,7 +18,7 @@ class TestPostgresExecuteAction:
         with pytest.raises(ValueError, match="Unknown action"):
             tool.execute_action("invalid")
 
-    @patch("application.agents.tools.postgres.psycopg.connect")
+    @patch("docsgpt.agents.tools.postgres.psycopg.connect")
     def test_select_query(self, mock_connect, tool):
         mock_conn = MagicMock()
         mock_cur = MagicMock()
@@ -37,7 +37,7 @@ class TestPostgresExecuteAction:
         assert result["response_data"]["data"][0] == {"id": 1, "name": "Alice"}
         mock_conn.close.assert_called_once()
 
-    @patch("application.agents.tools.postgres.psycopg.connect")
+    @patch("docsgpt.agents.tools.postgres.psycopg.connect")
     def test_insert_query(self, mock_connect, tool):
         mock_conn = MagicMock()
         mock_cur = MagicMock()
@@ -55,7 +55,7 @@ class TestPostgresExecuteAction:
         mock_conn.commit.assert_called_once()
         mock_conn.close.assert_called_once()
 
-    @patch("application.agents.tools.postgres.psycopg.connect")
+    @patch("docsgpt.agents.tools.postgres.psycopg.connect")
     def test_db_error(self, mock_connect, tool):
         import psycopg
 
@@ -68,7 +68,7 @@ class TestPostgresExecuteAction:
         assert result["status_code"] == 500
         assert "Database error" in result["error"]
 
-    @patch("application.agents.tools.postgres.psycopg.connect")
+    @patch("docsgpt.agents.tools.postgres.psycopg.connect")
     def test_get_schema(self, mock_connect, tool):
         mock_conn = MagicMock()
         mock_cur = MagicMock()
@@ -89,7 +89,7 @@ class TestPostgresExecuteAction:
         assert result["schema"]["users"][0]["column_name"] == "id"
         mock_conn.close.assert_called_once()
 
-    @patch("application.agents.tools.postgres.psycopg.connect")
+    @patch("docsgpt.agents.tools.postgres.psycopg.connect")
     def test_get_schema_db_error(self, mock_connect, tool):
         import psycopg
 
@@ -100,7 +100,7 @@ class TestPostgresExecuteAction:
         assert result["status_code"] == 500
         assert "Database error" in result["error"]
 
-    @patch("application.agents.tools.postgres.psycopg.connect")
+    @patch("docsgpt.agents.tools.postgres.psycopg.connect")
     def test_connection_closed_on_error(self, mock_connect, tool):
         import psycopg
 
@@ -114,7 +114,7 @@ class TestPostgresExecuteAction:
 
         mock_conn.close.assert_called_once()
 
-    @patch("application.agents.tools.postgres.psycopg.connect")
+    @patch("docsgpt.agents.tools.postgres.psycopg.connect")
     def test_select_with_no_description(self, mock_connect, tool):
         mock_conn = MagicMock()
         mock_cur = MagicMock()