atperson — scoped private-header atom names

Closed issue #42 (modularisation). The last two items:

• main.cpp thinning (96a3c66, devlog 2026-09-17-atperson-cli-atoms) — 500 → 231 lines, command bodies in src/app/cli/ atoms.
• Private-header atom-name shortening (7a63463) — headers that repeated their scope name now match their already-short implementation siblings: ingestion/policy.hpp, ingestion/state.hpp, resource/budget.hpp, resource/runtime.hpp, resource/system.hpp, state/lock.hpp, sync/engine.hpp, action/inspection.hpp, atproto/client.hpp, cli/graph.hpp, cli/ledger.hpp.

Header guards were already in the short form, so files now match their guards. Core-side ledger_internal.h and action_internal.h keep their names deliberately: renaming them to internal.h would shadow src/core/internal.h in quoted-include lookup. The audit scope was already short-named.

Include-only change; both configurations build and pass 33/33.