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/core/test_models_config_dir.py

@@ -15,7 +15,7 @@ from unittest.mock import MagicMock, patch
 
 import pytest
 
-from application.core.model_registry import ModelRegistry
+from docsgpt.core.model_registry import ModelRegistry
 
 
 def _make_settings(**overrides):
@@ -67,7 +67,7 @@ class TestOperatorAddsNewProvider:
         monkeypatch.setenv("FIREWORKS_API_KEY", "fw-key")
 
         s = _make_settings(MODELS_CONFIG_DIR=str(tmp_path))
-        with patch("application.core.settings.settings", s):
+        with patch("docsgpt.core.settings.settings", s):
             reg = ModelRegistry()
 
         m = reg.get_model("accounts/fireworks/models/llama-v3p3-70b-instruct")
@@ -99,7 +99,7 @@ class TestOperatorExtendsExistingProvider:
             ANTHROPIC_API_KEY="sk-ant",
             MODELS_CONFIG_DIR=str(tmp_path),
         )
-        with patch("application.core.settings.settings", s):
+        with patch("docsgpt.core.settings.settings", s):
             reg = ModelRegistry()
 
         # Built-in models still present
@@ -137,7 +137,7 @@ class TestOperatorOverridesBuiltinCapabilities:
             MODELS_CONFIG_DIR=str(tmp_path),
         )
         with caplog.at_level(logging.WARNING):
-            with patch("application.core.settings.settings", s):
+            with patch("docsgpt.core.settings.settings", s):
                 reg = ModelRegistry()
 
         m = reg.get_model("claude-haiku-4-5")
@@ -164,7 +164,7 @@ class TestMisconfiguredOperatorDir:
         s = _make_settings(MODELS_CONFIG_DIR=str(bogus))
 
         with caplog.at_level(logging.WARNING):
-            with patch("application.core.settings.settings", s):
+            with patch("docsgpt.core.settings.settings", s):
                 reg = ModelRegistry()
 
         # Built-in catalog still loaded
@@ -178,7 +178,7 @@ class TestMisconfiguredOperatorDir:
 
         s = _make_settings(MODELS_CONFIG_DIR=str(afile))
         with caplog.at_level(logging.WARNING):
-            with patch("application.core.settings.settings", s):
+            with patch("docsgpt.core.settings.settings", s):
                 reg = ModelRegistry()
 
         assert reg.get_model("docsgpt-local") is not None
@@ -199,7 +199,7 @@ class TestOperatorValidation:
         """))
 
         s = _make_settings(MODELS_CONFIG_DIR=str(tmp_path))
-        with patch("application.core.settings.settings", s):
+        with patch("docsgpt.core.settings.settings", s):
             with pytest.raises(Exception) as exc_info:
                 ModelRegistry()
         # Could be ModelYAMLError (enum check) or ValueError (registry check);