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.

deployment/docker-compose.yaml

@@ -32,7 +32,8 @@ services:
   backend:
     user: root
     build:
-      context: ../application
+      context: ..
+      dockerfile: docsgpt/Dockerfile
       args:
         # Optional extras to bake in (comma-separated): docling, milvus. The
         # docling extra brings the layout-model parser/OCR backend and its
@@ -57,9 +58,9 @@ services:
     ports:
       - "7091:7091"
     volumes:
-      - ../application/indexes:/app/indexes
-      - ../application/inputs:/app/inputs
-      - ../application/vectors:/app/vectors
+      - ../docsgpt/indexes:/app/indexes
+      - ../docsgpt/inputs:/app/inputs
+      - ../docsgpt/vectors:/app/vectors
     depends_on:
       redis:
         condition: service_started
@@ -69,7 +70,8 @@ services:
   worker:
     user: root
     build:
-      context: ../application
+      context: ..
+      dockerfile: docsgpt/Dockerfile
       args:
         EXTRAS: ${EXTRAS:-}
         INSTALL_DOCLING: ${INSTALL_DOCLING:-false}
@@ -80,7 +82,7 @@ services:
     # fails after EMBEDDINGS_DELEGATE_TIMEOUT, because EMBEDDINGS_DELEGATE_TO_WORKER
     # is on by default. For heavy/OCR parsing run a separate worker with `-Q parsing`;
     # to keep query latency off the ingest pool, another with `-Q embeddings`.
-    command: celery -A application.app.celery worker -l INFO -B -Q docsgpt,parsing,embeddings
+    command: celery -A docsgpt.app.celery worker -l INFO -B -Q docsgpt,parsing,embeddings
     env_file:
       - ../.env
     environment:
@@ -91,9 +93,9 @@ services:
       - CACHE_REDIS_URL=redis://redis:6379/2
       - POSTGRES_URI=postgresql://docsgpt:docsgpt@postgres:5432/docsgpt
     volumes:
-      - ../application/indexes:/app/indexes
-      - ../application/inputs:/app/inputs
-      - ../application/vectors:/app/vectors
+      - ../docsgpt/indexes:/app/indexes
+      - ../docsgpt/inputs:/app/inputs
+      - ../docsgpt/vectors:/app/vectors
     depends_on:
       redis:
         condition: service_started