adf migrate produces malformed core.adf with duplicate list markers and structural artifacts

[stackbilt-admin]

Description

When running charter adf migrate on a project with CLAUDE.md, .cursorrules, and agents.md pointer files, the migration merges content into core.adf with formatting issues:

1. Double/triple list markers: - - - Product: instead of - Product:
2. Module index table merged as content: The <!-- charter:module-index:start --> block from CLAUDE.md (a charter-generated rendering artifact) is treated as migratable CONTEXT content and inserted into core.adf
3. Pointer boilerplate merged as context: Phrases like "This file is intentionally thin" and "Primary instruction source:" are classified as CONTEXT — these are meta-instructions about the pointer file itself, not project rules

Steps to Reproduce

1. Have a project with existing .ai/ modules and agent config files (CLAUDE.md, .cursorrules, agents.md) that contain pointer text
2. Run charter adf migrate
3. Inspect .ai/core.adf — observe duplicate list markers and non-rule content in CONTEXT section

Expected Behavior

The migrate classifier should:

• Recognize <!-- charter:module-index:start --> ... <!-- charter:module-index:end --> blocks as structural, not migratable
• Recognize pointer boilerplate ("This file is intentionally thin", "Primary instruction source:", "Do not duplicate or extend agent policy here") as structural
• Produce clean single list markers in the target ADF file

Environment

• Charter v0.9.2
• pnpm monorepo on WSL2