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.

scripts/e2e/mock_llm.py

@@ -28,7 +28,7 @@ verbatim as the conversation's prompt). See
 
 Run standalone (does NOT import anything from ``application/``). Python 3.11+.
 Flask is the only non-stdlib dependency and is already in
-``application/requirements.txt``.
+``docsgpt/requirements.txt``.
 
 Usage::
 
@@ -482,7 +482,7 @@ def _stream_chat_response(
     if tool_calls and toolcall_arg_mode:
         # Frame-split mode: the call's ``arguments`` are spread over several
         # deltas that all share one ``index``, which is what the client-side
-        # merge in application/llm/handlers/base.py reassembles.
+        # merge in docsgpt/llm/handlers/base.py reassembles.
         call = tool_calls[0]
         frames = _toolcall_arg_frames(call["function"]["arguments"], toolcall_arg_mode)
         for position, piece in enumerate(frames):

scripts/e2e/mock_oidc_idp.py

@@ -20,7 +20,7 @@ comes from ``MOCK_OIDC_GROUPS`` (comma-separated).
 
 Run standalone (does NOT import anything from ``application/``). Dependencies
 (flask, python-jose, cryptography, requests) are all in
-``application/requirements.txt``.
+``docsgpt/requirements.txt``.
 
 Usage::
 

scripts/e2e/up.sh

@@ -255,7 +255,7 @@ FLASK_PID="$PIDDIR/flask.pid"
 log "starting Flask on 127.0.0.1:$FLASK_PORT"
 (
     cd "$E2E_TMP"
-    PYTHONUNBUFFERED=1 nohup "$FLASK_BIN" --app ../application/app.py run \
+    PYTHONUNBUFFERED=1 nohup "$FLASK_BIN" --app ../docsgpt/app.py run \
         --host 127.0.0.1 --port "$FLASK_PORT" \
         >"$FLASK_LOG" 2>&1 &
     echo $! > "$FLASK_PID"
@@ -275,7 +275,7 @@ log "starting Celery worker (solo pool)"
     cd "$E2E_TMP"
     PYTHONPATH="$REPO_ROOT${PYTHONPATH:+:$PYTHONPATH}" \
     PYTHONUNBUFFERED=1 \
-    nohup "$PY_BIN" -m celery -A application.app.celery worker \
+    nohup "$PY_BIN" -m celery -A docsgpt.app.celery worker \
         -l INFO --pool=solo -Q docsgpt,parsing \
         --without-gossip --without-mingle --without-heartbeat \
         >"$CELERY_LOG" 2>&1 &
@@ -290,7 +290,7 @@ if ! wait_for_log "celery 'celery@'" 30 "$CELERY_LOG" "celery@"; then
 fi
 
 # Ready check via `celery inspect ping`. We can't grep the log for 'ready'
-# because application/core/logging_config.py calls dictConfig with the default
+# because docsgpt/core/logging_config.py calls dictConfig with the default
 # disable_existing_loggers=True, which silences celery.worker's ready banner.
 # `inspect ping` queries the worker over the broker — it's the canonical
 # responsiveness check and doesn't depend on log output.
@@ -301,7 +301,7 @@ while (( elapsed < CELERY_INSPECT_TIMEOUT )); do
     if ( cd "$E2E_TMP" && \
          PYTHONPATH="$REPO_ROOT${PYTHONPATH:+:$PYTHONPATH}" \
          PYTHONUNBUFFERED=1 \
-         "$PY_BIN" -m celery -A application.app.celery inspect ping \
+         "$PY_BIN" -m celery -A docsgpt.app.celery inspect ping \
              --timeout 2 >/dev/null 2>&1 ); then
         ping_ok=1
         log "  -> celery inspect ping OK after ${elapsed}s"