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/llm/test_llama_cpp.py

@@ -1,4 +1,4 @@
-"""Unit tests for application/llm/llama_cpp.py — LlamaCpp and LlamaSingleton.
+"""Unit tests for docsgpt/llm/llama_cpp.py — LlamaCpp and LlamaSingleton.
 
 Covers:
   - LlamaSingleton: get_instance, query_model (thread-safe)
@@ -43,19 +43,19 @@ def patch_llama_cpp(monkeypatch):
     sys.modules["llama_cpp"] = fake_mod
 
     # Clear any cached instances
-    if "application.llm.llama_cpp" in sys.modules:
-        del sys.modules["application.llm.llama_cpp"]
+    if "docsgpt.llm.llama_cpp" in sys.modules:
+        del sys.modules["docsgpt.llm.llama_cpp"]
 
     yield
 
     sys.modules.pop("llama_cpp", None)
-    if "application.llm.llama_cpp" in sys.modules:
-        del sys.modules["application.llm.llama_cpp"]
+    if "docsgpt.llm.llama_cpp" in sys.modules:
+        del sys.modules["docsgpt.llm.llama_cpp"]
 
 
 @pytest.fixture
 def fresh_singleton():
-    from application.llm.llama_cpp import LlamaSingleton
+    from docsgpt.llm.llama_cpp import LlamaSingleton
 
     LlamaSingleton._instances = {}
     return LlamaSingleton
@@ -63,7 +63,7 @@ def fresh_singleton():
 
 @pytest.fixture
 def llm(fresh_singleton):
-    from application.llm.llama_cpp import LlamaCpp
+    from docsgpt.llm.llama_cpp import LlamaCpp
 
     instance = LlamaCpp(api_key="k", user_api_key=None, llm_name="/path/to/model")
     return instance
@@ -118,7 +118,7 @@ class TestLlamaCppConstructor:
         assert llm.api_key == "k"
 
     def test_sets_user_api_key(self):
-        from application.llm.llama_cpp import LlamaCpp, LlamaSingleton
+        from docsgpt.llm.llama_cpp import LlamaCpp, LlamaSingleton
 
         LlamaSingleton._instances = {}
         instance = LlamaCpp(