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/parser/file/test_openapi3_parser.py

@@ -1,4 +1,4 @@
-"""Tests for application.parser.file.openapi3_parser covering lines 7-8, 45."""
+"""Tests for docsgpt.parser.file.openapi3_parser covering lines 7-8, 45."""
 
 import pytest
 from unittest.mock import MagicMock, patch
@@ -9,16 +9,16 @@ class TestOpenAPI3ParserImportFallback:
     def test_import_fallback_to_base_parser(self):
         """Cover lines 7-8: try/except ModuleNotFoundError import fallback."""
         # The fallback import is a module-level concern. Just verify the class works.
-        with patch("application.parser.file.openapi3_parser.parse"):
-            from application.parser.file.openapi3_parser import OpenAPI3Parser
+        with patch("docsgpt.parser.file.openapi3_parser.parse"):
+            from docsgpt.parser.file.openapi3_parser import OpenAPI3Parser
 
             parser = OpenAPI3Parser()
             assert parser is not None
 
     def test_get_base_urls(self):
         """Cover basic URL extraction."""
-        with patch("application.parser.file.openapi3_parser.parse"):
-            from application.parser.file.openapi3_parser import OpenAPI3Parser
+        with patch("docsgpt.parser.file.openapi3_parser.parse"):
+            from docsgpt.parser.file.openapi3_parser import OpenAPI3Parser
 
             parser = OpenAPI3Parser()
             urls = parser.get_base_urls([
@@ -32,8 +32,8 @@ class TestOpenAPI3ParserImportFallback:
 
     def test_get_info_from_paths_empty(self):
         """Cover path with no operations."""
-        with patch("application.parser.file.openapi3_parser.parse"):
-            from application.parser.file.openapi3_parser import OpenAPI3Parser
+        with patch("docsgpt.parser.file.openapi3_parser.parse"):
+            from docsgpt.parser.file.openapi3_parser import OpenAPI3Parser
 
             parser = OpenAPI3Parser()
             mock_path = MagicMock()
@@ -43,8 +43,8 @@ class TestOpenAPI3ParserImportFallback:
 
     def test_parse_file_writes_results(self, tmp_path):
         """Cover line 45: parse_file writes to results.txt."""
-        with patch("application.parser.file.openapi3_parser.parse") as mock_parse:
-            from application.parser.file.openapi3_parser import OpenAPI3Parser
+        with patch("docsgpt.parser.file.openapi3_parser.parse") as mock_parse:
+            from docsgpt.parser.file.openapi3_parser import OpenAPI3Parser
 
             mock_server = MagicMock()
             mock_server.url = "https://api.example.com"