v1.4.8 — agent-experience inbox + messaging fixes

Highlights

• Non-destructive reads (TSU-73): get_inbox no longer marks-read-on-fetch or truncates a P0 — mark_read is explicit, first read returns full content. Stops silent message loss.
• Reply-path grant (TSU-75): receiving a DM grants a scoped, time-boxed path to reply back across the auth-wall — no more detours when answering a P0 sent to you.

#120, #121.