refactor(preset): rename the generic preset to auto

[izzet]

Renames the generic analyzer preset to auto, which better describes what it does: it discovers one layer per distinct cat in the trace rather than being a generic fallback.

• AnalyzerPresetConfigGeneric → AnalyzerPresetConfigAuto
• config group value analyzer/preset=generic → analyzer/preset=auto
• tests/test_generic_preset_e2e.py → tests/test_auto_preset_e2e.py (via git mv, 92% similarity), plus the test_generic_preset_* function names in it and in test_category_layers.py
• documents auto in docs/configuration.rst, which previously listed only posix and dlio

No backward-compatible alias

Deliberate. The preset landed in #61, one commit before this branch point — it has never appeared in a tagged release, in the docs, or in CI, so there is no installed base of preset=generic invocations. An alias would also be misleading: the node's own name field is now auto, so preset=generic would resolve to a preset that reports itself as auto. Hydra's error already lists the valid options:

In 'config': Could not find 'analyzer/preset/generic'
Available options in 'analyzer/preset':
	auto
	dlio
	dlio-prev
	posix

Note that generic also appears in unrelated contexts (e.g. self.generic_visit(node), a Python ast API) which are untouched.

Verification

• pytest -m smoke — 155 passed, 32 deselected
• pytest tests/test_auto_preset_e2e.py tests/test_category_layers.py — 52 passed
• CLI with analyzer/preset=auto produces a populated layer breakdown with the auto-discovered category layers

Merge order

Please merge before the dlio/ai preset rename, which builds on this branch and touches the same preset registry. Until this merges, that PR will also display these commits.