chore: switch to ruff + pydoclint, deprecate .gitingest, and perform a repo-wide quality sweep

[filipchristiansen]

Consolidates our lint/format tooling around Ruff, deprecates the old .gitingest spec, and sweeps the codebase for consistency & hidden bugs (no functional API changes).

Area	Key changes
Pre-commit	black / darglint hooks → ruff-check & ruff-format New docstring linter: pydoclint
Dependencies	Drop tomli; tighten typing_extensions; add eval-type-backport Remove black, djlint, pylint from requirements-dev
Ignore handling	Deprecate .gitingest (TOML) New .gitingestignore using git-wildmatch (parses via existing _parse_ignore_file)
Tooling / config	New [tool.ruff] section (lint + format + isort rules) Remove [tool.black]; keep minimal [tool.isort] for now
Refactor / style	from __future__ import annotations, kw-only args, richer types Re-order params & __all__, move type-only imports under if TYPE_CHECKING Extract CLI args to TypedDict[_CLIArgs]; form data to pydantic.QueryForm Deduplicate cli.main / _async_main & split large functions pathlib everywhere, no file-IO in async, constants > magic numbers Delete is_text_file – logic now lives in FileSystemNode.content
Bug fix	Eliminated silent bug in notebook_utils._process_cell
Docs / badges	README badge refresh
Tests	Updated fixtures & assertions

⚠️ Breaking changes

• New file: .gitingestignore (drop-in git-wildmatch).
  Existing .gitingest is now deprecated.

No other functional API or CLI changes.

[cyclotruc]

Much needed cleanup after dropping Python 3.7 support, thanks @filipchristiansen