[Python] fd5 edit CLI command with audit logging

[gerchowl]

Parent: #161

Goal

Add fd5 edit CLI subcommand that modifies an attribute and appends an audit log entry.

Spec

• fd5 edit <file> <path>.<attr> <value> [--message MSG] [--in-place]
• Default: copy-on-write (creates _edited.h5 copy)
• --in-place: edit original file
• --message/-m: commit message (optional, defaults to "Edit .")
• Reads identity from ~/.fd5/identity.toml
• Creates AuditEntry with: parent_hash, timestamp, author, message, changes
• Appends entry to _fd5_audit_log, then recomputes content_hash

Flow

1. Open file (copy or in-place)
2. Read current content_hash → parent_hash
3. Read current attribute value → old
4. Write new attribute value
5. Append AuditEntry to _fd5_audit_log
6. Recompute and write content_hash

TDD

• Test edit creates audit entry
• Test edit preserves existing audit log entries
• Test copy-on-write creates new file
• Test in-place modifies original
• Test message defaults
• Test identity is recorded