adf fmt should normalize migrate artifacts (duplicate markers, non-ADF content)

[stackbilt-admin]

Description

After charter adf migrate introduces formatting issues in .adf files (duplicate list markers like - - -, HTML comment blocks, markdown tables in CONTEXT sections), charter adf fmt --write would be the natural fix. However, fmt doesn't catch these structural issues.

Examples of artifacts fmt should normalize

1. Duplicate list markers: - - - Product: → - Product:
2. HTML comments in ADF sections: <!-- charter:module-index:start --> inside CONTEXT blocks should be stripped
3. Markdown tables in ADF sections: Table syntax (| Module | Triggers |) is not valid ADF content and should be flagged or removed
4. Dangling references: Bare lines like - \.ai/manifest.adf`` in CONSTRAINTS that are pointer artifacts, not actual constraints

Expected Behavior

If adf fmt is the canonical normalizer for ADF files, it should:

• Collapse consecutive list markers (- - - → -)
• Strip HTML comments from ADF section bodies
• Flag or remove non-ADF content (markdown tables, raw URLs without context)
• Produce clean, parseable ADF output

This would serve as a safety net for migrate/tidy artifacts and also help users who hand-edit .adf files.

Environment

• Charter v0.9.2

[stackbilt-admin]

Already fixed in 6f921bf — fmt normalizes duplicate list markers, strips HTML comments, and removes markdown tables from ADF sections.