Add structured recovery diagnostics

[johnny-emp]

Summary

• add typed recovery integrity diagnostics for manifest-referenced WAL segment issues
• surface missing segment, missing size/checksum metadata, checksum mismatch, truncation, and size mismatch as structured kinds
• add a recovery outcome API for permissive-mode skipped-segment warnings while keeping checksum corruption fail-closed

Tests

• cargo test recovery::
• cargo test --test crash_matrix crash_matrix_corrupt_wal_frame_fails_closed_in_permissive_mode
• cargo test --test naming_conventions
• cargo test