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.

docs/content/Guides/Customising-prompts.mdx

@@ -359,7 +359,7 @@ Technical documentation about...
 ### Template Validation
 Test your template syntax before saving:
 ```python
-from application.api.answer.services.prompt_renderer import PromptRenderer
+from docsgpt.api.answer.services.prompt_renderer import PromptRenderer
 
 renderer = PromptRenderer()
 is_valid = renderer.validate_template("Your prompt with {{ variables }}")
@@ -487,7 +487,7 @@ Provide detailed answers appropriate for {{ passthrough.access_level }} access l
 
 ### Render Prompt via API
 ```python
-from application.api.answer.services.prompt_renderer import PromptRenderer
+from docsgpt.api.answer.services.prompt_renderer import PromptRenderer
 
 renderer = PromptRenderer()
 rendered = renderer.render_prompt(

docs/content/Guides/compression.md

@@ -19,7 +19,7 @@ The compression system operates on a "summarize and truncate" principle:
 
 ## Configuration
 
-You can configure the compression behavior in your `.env` file or `application/core/settings.py`:
+You can configure the compression behavior in your `.env` file or `docsgpt/core/settings.py`:
 
 | Setting | Default | Description |
 | :--- | :--- | :--- |

docs/content/Guides/ocr.mdx

@@ -57,7 +57,7 @@ apt-get install tesseract-ocr tesseract-ocr-eng    brew install tesseract
 Docker images build without it by default; opt in with the build argument:
 
 ```bash
-docker build --build-arg INSTALL_TESSERACT=true ./application
+docker build -f docsgpt/Dockerfile --build-arg INSTALL_TESSERACT=true .
 ```
 
 `deployment/docker-compose.yaml` forwards the same switch, so setting
@@ -94,7 +94,7 @@ docling is not part of the base install, and OCR does not need it (see
 output:
 
 ```bash
-pip install -r application/requirements-docling.txt   # or: uv sync --extra docling
+pip install -r docsgpt/requirements-docling.txt   # or: uv sync --extra docling
 ```
 
 That file is the core set plus the `docling` extra, exported from the same
@@ -108,7 +108,7 @@ layout, table-structure and RapidOCR models in so the first parse does not
 download them. Local builds opt in with the build argument:
 
 ```bash
-docker build --build-arg EXTRAS=docling ./application
+docker build -f docsgpt/Dockerfile --build-arg EXTRAS=docling .
 ```
 
 `deployment/docker-compose.yaml` forwards the same switch, so setting