fix: paste-safe multi-line value input in pos ai alias Insert Prompt

menu_ask_value used line-oriented read -rp: a multiline Ctrl+V paste
flooded the tty queue, read consumed only the first line, and the rest
executed as commands later (or were eaten by a later prompt).

- lib/menu-lib.sh: new menu_read_value() raw-mode bracketed-paste
  reader (stty -icanon -echo -isig, \e[?2004h/l, literal newlines inside
  [200~..[201~, Enter submits outside paste, edit keys, cancel on
  Ctrl-D-empty/Ctrl-C/Z/\, terminal restored via trap). Bytes via
  dd|od|tr chunks, not bash read: read self-interrupts on ETX from a
  tty even with ISIG disabled.
- bin/pos-ai-alias: prompt encode/decode (backslash, newline) with
  load/save wiring; newline-safe truncate; edit wizard Enter keeps the
  full original prompt (no more silent >80-char truncation).

Verified via pty harnesses: multiline + single-line paste captured
verbatim with nothing executed, Ctrl-D/Ctrl-C cancel cleanly, full
create/list/show/edit E2E, round-trips byte-exact. Gates: make gen &&
make check, make lint 0 FAIL 0 WARN.

DOC/AGENT_Context_Project.md

@@ -594,7 +594,7 @@ Use conventional prefixes: `feat:`, `fix:`, `docs:`, `refactor:`, `chore:`
 | `lib/user-timers-lib.sh` | 112 | Shared systemd **user** timer machinery (interval→OnCalendar, unit pair writer, linger) |
 | `lib/usb-lib.sh` | 205 | Shared USB-storage detection + pick flow (detect/mount-offer/`usb_pick_root`; EFI system partitions excluded; picker shows size/label/fs) — used by `pos system backup` + `pos media sync` |
 | `lib/share-lib.sh` | 318 | Domain layer for the share suite (usbsrv/smbclient record parsers, folder+mountpoint candidates, remote listings, service/firewall advisories; EOF-safe) + compat shims to `lib/menu-lib.sh` — used by all five `pos share *` tools |
-| `lib/menu-lib.sh` | 169 | Category-neutral interactive menu primitives (`menu_guard` tty guard, `menu_run` looping boxed menu, `menu_pick` type-to-filter picker, `menu_ask_value` prompt-with-default; stderr render, fail-closed on non-tty/EOF) — sourced by `share-lib.sh`, open to any category |
+| `lib/menu-lib.sh` | 362 | Category-neutral interactive menu primitives (`menu_guard` tty guard, `menu_run` looping boxed menu, `menu_pick` type-to-filter picker, `menu_ask_value` prompt-with-default via raw-mode bracketed-paste-safe `menu_read_value`; stderr render, fail-closed on non-tty/EOF) — sourced by `share-lib.sh`, open to any category |
 | `lib/registry.sh` | 199 | Shared query API for POS tool metadata headers (`# POS_*:`) — `reg_scan`/`reg_list`/`reg_lookup`/`reg_each`/config scope helpers; used by `pos-tree` and `gen-docs.sh` |
 | `bin/flag-reader` | 58 | Inspect flags (list/status/`--raw`) |
 | `bin/flag-set` | 21 | Set a flag (optionally with a value) |
@@ -603,7 +603,7 @@ Use conventional prefixes: `feat:`, `fix:`, `docs:`, `refactor:`, `chore:`
 | `features/usb-automount.sh` | 138 | USB automount feature (udev rule + flag-gated service) |
 <!-- GEN:START filetable -->
 | `bin/pos` | 302 | CLI dispatcher with smart arg matching + logging + category help |
-| `bin/pos-ai-alias` | 712 | manage AI agent aliases |
+| `bin/pos-ai-alias` | 760 | manage AI agent aliases |
 | `bin/pos-ai-gemini` | 7 | Forward to pos ai --provider gemini (backward compat) |
 | `bin/pos-ai-openrouter` | 7 | Forward to pos ai --provider openrouter (backward compat) |
 | `bin/pos-communication-matrix-listener` | 568 | Matrix listener: map /command → bash, run them on room messages |