Feat/prompt+auth

[cachebag]

Summary

• Prompt float now treats <CR> as a newline so multi-line instructions no longer fight the UI; submit moves to <C-CR> (insert) and <CR> (normal).
• Adds in-session prompt history: <Up> / <Down> recall previously submitted prompts (including @file mentions as typed).
• Keeps completion-menu behavior intact — <CR> still confirms the pum, and Up/Down navigate it while open.

Details

• History is a session-scoped ring (max 50), skips empty and consecutive-duplicate entries, and preserves the in-progress draft when you start cycling.
• First <Up> stashes the current draft and restores it once you page back past the newest entry.
• Float title shows a · Ctrl-CR submit hint for discoverability.
• README Use section updated for the new keybinds.

Note: some terminals don't send a distinct <C-CR>; there, use normal-mode <CR> (Esc then Enter) to submit.