atperson unified internal headers

Following the persistence modularisation, consolidate each core scope behind a single unified internal header that all of the scope's atoms include.

Changes

• persistence/persistence_internal.h: single scope-private header consolidating includes and all internal type definitions (atp_buffer, atp_section_writer, atp_reader, atp_section) and function declarations. All 8 persistence atoms include only this header.
• graph/graph_internal.h: same pattern for the 7 graph atoms (lifecycle, index, groups, store, observe, query, valence).
• action/action_internal.h: same pattern for the 4 action atoms (candidates, plans, ordering, guard).
• Deleted the superseded per-atom persistence headers (format.h, reader.h, wire.h, sections.h, v5.h, v6.h, migration.h) after folding the wire-format identifiers into the unified header.

Verification

All three CI configs (network ON/OFF, ASan) 49/49 green.

Commits: ae92c81, 060ca7b, d9484f5