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.

docsgpt/api/user/me/__init__.py

@@ -0,0 +1,3 @@
+from .routes import me_ns
+
+__all__ = ["me_ns"]

docsgpt/api/user/me/routes.py

@@ -0,0 +1,34 @@
+"""Current-principal endpoint.
+
+``GET /api/user/me`` returns the caller's user id and resolved roles, sourced
+only from ``request.decoded_token`` (already populated and role-resolved by the
+auth chokepoint in ``app.py``). Auth-mode-agnostic. ``email``/``name``/
+``picture`` are OIDC-only and optional — they are echoed from the token and are
+never present for ``simple_jwt``/``session_jwt``/no-auth modes.
+"""
+
+from __future__ import annotations
+
+from flask import jsonify, make_response, request
+from flask_restx import Namespace, Resource
+
+me_ns = Namespace("me", description="Current user identity and roles", path="/api")
+
+
+@me_ns.route("/user/me")
+class MeResource(Resource):
+    def get(self):
+        """Return ``{user_id, roles, email?, name?, picture?}`` for the caller."""
+        decoded_token = getattr(request, "decoded_token", None)
+        if not decoded_token:
+            return make_response(jsonify({"success": False}), 401)
+        body = {
+            "success": True,
+            "user_id": decoded_token.get("sub"),
+            "roles": decoded_token.get("roles") or ["user"],
+        }
+        for field in ("email", "name", "picture"):
+            value = decoded_token.get(field)
+            if value:
+                body[field] = value
+        return make_response(jsonify(body), 200)