feat: add AOMIC-PIOP1 dataset support

[MarioAderman]

Description

Add support for AOMIC-PIOP1 dataset (OpenNeuro ds002785) with 216 healthy adult subjects.

Implements Issue #12.

Changes

Core Implementation:

• src/bids_hub/datasets/aomic_piop1.py - Dataset module with T1w, DWI, BOLD support
• src/bids_hub/validation/aomic.py - Validation config (expected counts from Scientific Data paper)
• CLI commands: bids-hub aomic piop1 [build|validate|info]

Testing:

• tests/test_aomic_piop1.py - 19 tests with 93% module coverage
• Synthetic BIDS fixture with 3 test subjects (full/minimal/missing)
• Improved type checking practices (explicit string vs Path assertions)

Documentation:

• docs/dataset-cards/aomic-piop1.md - Complete dataset card
• scripts/download_aomic_piop1.sh - Download script with 3 methods
• Updated CLAUDE.md with AOMIC-PIOP1 commands and schema

Integration:

• Updated exports in __init__.py files
• Added coverage.xml to .gitignore

Dataset Details

• Source: OpenNeuro ds002785
• Paper: Snoek et al., Scientific Data 2021
• License: CC0 (Public Domain)
• Subjects: 216 healthy adults (after QC)
• Modalities: T1w (single), DWI (multiple runs), BOLD (resting-state + tasks)

Testing

• ✅ All 97 tests pass (78 existing + 19 new)
• ✅ Type checking: 0 errors (mypy strict)
• ✅ Linting: 0 errors (ruff)
• ✅ Formatting: All files formatted
• ✅ make all passes

Closes #12

[MarioAderman]

@CloseChoice @The-Obstacle-Is-The-Way Hey! just a quick win to add this dataset.

• Followed the work pattern of @The-Obstacle-Is-The-Way.
• Double-checked it and it's pretty solid tbh.

Any comments, let me know!

[The-Obstacle-Is-The-Way]

Hey @MarioAderman,

Great work here - solid implementation, comprehensive tests, and you followed the existing patterns well.

Quick note on a confusing situation: I maintain a fork (The-Obstacle-Is-The-Way/neuroimaging-go-brrrr) that has diverged from this repo with schema changes and validation improvements. I've integrated your AOMIC-PIOP1 work into my fork with full author attribution:

The-Obstacle-Is-The-Way@8517c4d

This doesn't affect your PR here - that's for @CloseChoice to decide. Just wanted to be transparent and let you know your contribution is already being used.

Thanks for the work.