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/test_memory_tool.py

@@ -12,7 +12,7 @@ from contextlib import contextmanager
 
 import pytest
 
-from application.agents.tools.memory import MemoryTool
+from docsgpt.agents.tools.memory import MemoryTool
 
 
 class _FakeMemoriesRepo:
@@ -83,13 +83,13 @@ def _noop_conn():
 def _patch(monkeypatch) -> None:
     _FakeMemoriesRepo.reset()
     monkeypatch.setattr(
-        "application.agents.tools.memory.MemoriesRepository", _FakeMemoriesRepo
+        "docsgpt.agents.tools.memory.MemoriesRepository", _FakeMemoriesRepo
     )
     monkeypatch.setattr(
-        "application.agents.tools.memory.db_session", _noop_conn
+        "docsgpt.agents.tools.memory.db_session", _noop_conn
     )
     monkeypatch.setattr(
-        "application.agents.tools.memory.db_readonly", _noop_conn
+        "docsgpt.agents.tools.memory.db_readonly", _noop_conn
     )