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/core/log_context.py

@@ -0,0 +1,57 @@
+"""Per-activity logging context backed by ``contextvars``.
+
+The ``_ContextFilter`` installed by ``logging_config.setup_logging`` stamps
+every ``LogRecord`` emitted inside a ``bind`` block with the bound keys, so
+they land as first-class attributes on the OTLP log export rather than being
+buried inside formatted message bodies.
+
+A single ``ContextVar`` holds a dict so nested binds reset atomically (LIFO)
+via the token returned by ``bind``.
+"""
+
+from __future__ import annotations
+
+from contextvars import ContextVar, Token
+from typing import Mapping
+
+
+_CTX_KEYS: frozenset[str] = frozenset(
+    {
+        "activity_id",
+        "parent_activity_id",
+        "user_id",
+        "agent_id",
+        "conversation_id",
+        "endpoint",
+        "model",
+    }
+)
+
+_ctx: ContextVar[Mapping[str, str]] = ContextVar("log_ctx", default={})
+
+
+def bind(**kwargs: object) -> Token:
+    """Overlay the given keys onto the current context.
+
+    Returns a ``Token`` so the caller can ``reset`` in a ``finally`` block.
+    Keys outside :data:`_CTX_KEYS` are silently dropped (so a typo can't
+    stamp a stray field name onto every record), as are ``None`` values
+    (a missing attribute is more useful than the literal string ``"None"``).
+    """
+    overlay = {
+        k: str(v)
+        for k, v in kwargs.items()
+        if k in _CTX_KEYS and v is not None
+    }
+    new = {**_ctx.get(), **overlay}
+    return _ctx.set(new)
+
+
+def reset(token: Token) -> None:
+    """Restore the context to the snapshot captured by the matching ``bind``."""
+    _ctx.reset(token)
+
+
+def snapshot() -> Mapping[str, str]:
+    """Return the current context dict. Treat as read-only; use :func:`bind`."""
+    return _ctx.get()