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/tools/test_api_body_serializer.py

@@ -1,4 +1,4 @@
-"""Comprehensive tests for application/agents/tools/api_body_serializer.py
+"""Comprehensive tests for docsgpt/agents/tools/api_body_serializer.py
 
 Covers: ContentType enum, RequestBodySerializer (JSON, form-urlencoded,
 multipart, text/plain, XML, octet-stream, unknown types), encoding rules,
@@ -10,7 +10,7 @@ from urllib.parse import parse_qs
 
 import pytest
 
-from application.agents.tools.api_body_serializer import (
+from docsgpt.agents.tools.api_body_serializer import (
     ContentType,
     RequestBodySerializer,
 )
@@ -561,7 +561,7 @@ class TestApiBodySerializerMultipartParts:
 
     def test_multipart_field_name_not_percent_encoded(self):
         """RFC 7578: names are a quoted string, so 'file name' stays literal."""
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             RequestBodySerializer,
         )
 
@@ -575,7 +575,7 @@ class TestApiBodySerializerMultipartParts:
         assert "file%20name" not in result
 
     def test_multipart_field_name_escapes_quotes_and_newlines(self):
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             RequestBodySerializer,
         )
 
@@ -589,7 +589,7 @@ class TestApiBodySerializerMultipartParts:
 
     def test_multipart_dict_unknown_content_type(self):
         """Cover line 226: dict with unknown content type uses str()."""
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             RequestBodySerializer,
         )
 
@@ -604,7 +604,7 @@ class TestApiBodySerializerMultipartParts:
 
     def test_multipart_string_json_content_type(self):
         """Cover line 229: string value with application/json content type."""
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             RequestBodySerializer,
         )
 
@@ -619,7 +619,7 @@ class TestApiBodySerializerMultipartParts:
 
     def test_multipart_string_xml_content_type(self):
         """Cover line 229: string value with application/xml content type."""
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             RequestBodySerializer,
         )
 
@@ -634,7 +634,7 @@ class TestApiBodySerializerMultipartParts:
 
     def test_multipart_string_unknown_content_type(self):
         """Cover line 229: string with unknown content type falls through."""
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             RequestBodySerializer,
         )
 
@@ -653,7 +653,7 @@ class TestApiBodySerializerOctetStreamCoverage:
 
     def test_octet_stream_bytes_input(self):
         """Cover line 271: _serialize_octet_stream with bytes input."""
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             ContentType,
             RequestBodySerializer,
         )
@@ -664,7 +664,7 @@ class TestApiBodySerializerOctetStreamCoverage:
 
     def test_octet_stream_string_input(self):
         """Cover line 275: _serialize_octet_stream with string input."""
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             ContentType,
             RequestBodySerializer,
         )
@@ -677,7 +677,7 @@ class TestApiBodySerializerOctetStreamCoverage:
         """Cover line 279: _serialize_octet_stream with dict input (fallback to JSON)."""
         import json
 
-        from application.agents.tools.api_body_serializer import (
+        from docsgpt.agents.tools.api_body_serializer import (
             ContentType,
             RequestBodySerializer,
         )