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/parser/file/base_parser.py

@@ -0,0 +1,133 @@
+"""Base parser and config class."""
+
+import importlib.util
+import logging
+import sys
+from abc import abstractmethod
+from pathlib import Path
+from typing import Dict, List, Optional, Union
+
+logger = logging.getLogger(__name__)
+
+
+class DocumentParseError(Exception):
+    """A file could not be converted to text.
+
+    Raised instead of returning the failure message as the document body: a
+    parser that hands back its own traceback produces an attachment/source
+    whose "content" is an error string, which then reaches the LLM as if it
+    were the document. Callers should treat this as a failed upload and tell
+    the user, rather than storing anything.
+
+    Deterministic for a given input, so it is marked non-retryable on the
+    Celery tasks that parse (alongside ``DataError`` and
+    ``AttachmentRejectedError``) — a poison file fails once instead of
+    re-failing identically on every retry.
+    """
+
+
+class BaseParser:
+    """Base class for all parsers."""
+
+    def __init__(self, parser_config: Optional[Dict] = None):
+        """Init params."""
+        self._parser_config = parser_config
+
+    def init_parser(self) -> None:
+        """Init parser and store it."""
+        parser_config = self._init_parser()
+        self._parser_config = parser_config
+
+    @property
+    def parser_config_set(self) -> bool:
+        """Check if parser config is set."""
+        return self._parser_config is not None
+
+    @property
+    def parser_config(self) -> Dict:
+        """Check if parser config is set."""
+        if self._parser_config is None:
+            raise ValueError("Parser config not set.")
+        return self._parser_config
+
+    @abstractmethod
+    def _init_parser(self) -> Dict:
+        """Initialize the parser with the config."""
+
+    @abstractmethod
+    def parse_file(self, file: Path, errors: str = "ignore") -> Union[str, List[str]]:
+        """Parse file."""
+
+    def get_file_metadata(self, file: Path) -> Dict:
+        """Return parser-specific metadata for the most recently parsed file."""
+        _ = file
+        return {}
+
+
+def module_available(name: str) -> bool:
+    """Whether top-level module ``name`` can be imported, without importing it.
+
+    Cheap enough to call while building a parser map. Honors ``sys.modules``
+    first so tests that stub a module in (or block one out with ``None``)
+    are seen the same way the import system would see them; a stub with no
+    ``__spec__`` counts as present rather than raising.
+
+    Args:
+        name: Top-level module name, e.g. ``"docling"``.
+
+    Returns:
+        True when an import of ``name`` would succeed.
+    """
+    if name in sys.modules:
+        return sys.modules[name] is not None
+    try:
+        return importlib.util.find_spec(name) is not None
+    except (ImportError, ValueError):
+        return False
+
+
+def delegate_parse(
+    parser: "BaseParser", file: Path, errors: str
+) -> Union[str, List[str]]:
+    """Run a fallback parser, normalizing its failures to ``DocumentParseError``.
+
+    Used wherever one parser hands a file to another (docling to the plain
+    tabular parsers for oversized sheets, anydoc to docling/legacy parsers
+    for files it cannot convert). Wrapping matters twice over: the Celery
+    tasks that own these paths list ``DocumentParseError`` in
+    ``dont_autoretry_for``, so a deterministic content error fails once
+    instead of retrying four times; and ``SimpleDirectoryReader.load_data``
+    catches only ``DocumentParseError``, so one poison file is skipped into
+    ``failed_files`` instead of aborting an entire multi-file ingest.
+
+    Args:
+        parser: The parser to delegate to; initialized here if needed.
+        file: Path to the file being parsed.
+        errors: Decoding error policy, forwarded to the parser.
+
+    Returns:
+        The parsed text, or list of row strings.
+
+    Raises:
+        DocumentParseError: If the fallback parser fails for any reason.
+    """
+    try:
+        if not parser.parser_config_set:
+            parser.init_parser()
+        return parser.parse_file(file, errors)
+    except DocumentParseError:
+        raise
+    except ImportError:
+        # A fallback whose dependency is missing is a deployment problem, not
+        # a bad document: let it reach the ingest task's setup-error path
+        # instead of blaming every file with "could not be read".
+        raise
+    except Exception as e:
+        logger.error(
+            f"Fallback parse of {Path(file).name} with "
+            f"{type(parser).__name__} failed: {e}",
+            exc_info=True,
+        )
+        raise DocumentParseError(
+            f"Failed to parse {Path(file).name}: the file could not be read."
+        ) from e