docs: describe prompt notifications

A prompt that waits on the human is announced after a grace period, and the
notification can carry the answer: allow / deny / review buttons for a
confirmation, a reply field for an `ask_user_line`. `doc/notifications.md` lays
out the two channels (the optional `desktop-notifier` extra, and OSC 777 / OSC 9
written to `/dev/tty` with no dependency), what each prompt kind offers, why the
reason line stays out by default, and the platform limits — no buttons where a
server does not render them, a reply field only under KDE, kitty left with the
bell.

The example config and the README config block gain the `[notify]` section, and
AGENTS.md documents the three prompt hooks and the rule that only the outermost
prompt of a nested read is announced.

doc/notifications.md

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+# Prompt notifications
+
+A turn stops while a prompt waits on the human. If you switched to another
+window, the wait is invisible until you come back — so the CLI announces it.
+
+A prompt is announced only after `grace_seconds` of waiting (5s by default), so
+answering at the terminal stays silent. Bursts are throttled by
+`min_interval_seconds`, and the announcement says what is being asked, not what
+it would run: the one-line reason can name a command, argv or URL, and a
+notification outlives the prompt (and may be mirrored to a lock screen), so it
+travels only with `include_reason = true`.
+
+## Configuration
+
+```toml
+[notify]
+enabled = true
+grace_seconds = 5.0
+min_interval_seconds = 10.0
+channels = ["auto"]        # auto | desktop | terminal
+actions = true             # offer the answer, not just the news
+include_reason = false
+protocol = ""              # terminal protocol override: osc777 / osc9 / bell
+```
+
+`channels = ["auto"]` tries the desktop first and falls back to the terminal;
+`["desktop"]` and `["terminal"]` pin one of them. Notifications are only sent
+from an interactive run — a one-shot `plyngent "…"` never waits on a human, and
+a prompt answered inside the grace period is never announced at all.
+
+## What is answered where
+
+| Prompt | Notification offers |
+|---|---|
+| tool confirm (single / a round's batch) | Allow once / Deny / Go to terminal |
+| command denylist, `fetch_local` private host | same three |
+| directory-access request, skill write | same three |
+| `ask_user_line` | a reply field — the answer *is* the text you type |
+| `ask_user_choice`, `ask_user_form`, PTY secrets | nothing (terminal only) |
+| limit-continue | nothing (terminal only) |
+
+An answer read from the notification is treated exactly like a typed one —
+`allow` is the `y` the prompt accepts, `deny` is `n` — and it never records a
+session grant: the button means "this once". "Go to terminal" withdraws the
+notification and leaves the prompt waiting. A secret is never asked for in a
+notification, and never echoed into one.
+
+## Desktop channel
+
+The desktop channel needs the optional extra:
+
+```console
+pip install 'plyngent[notify]'
+```
+
+It wraps `desktop-notifier`, which talks to `org.freedesktop.Notifications` on
+Linux, Notification Center on macOS and WinRT on Windows. Buttons need a
+notification server that renders them (KDE Plasma and GNOME Shell do; a bare
+`dunst` may not, and then the notification is text-only without any error). The
+reply field is KDE-only in practice: it is the `inline-reply` capability plus the
+`x-kde-reply-submit-button-text` hint, which only KNotifications implements.
+
+Notifications are shown from the library's async API on a loop that runs in a
+daemon thread, because callbacks only fire while the loop that owns the
+notification is running.
+
+## Terminal channel
+
+No dependency and no extra: the CLI writes an escape sequence to `/dev/tty`
+(never stdout, so a redirect cannot swallow it) and the terminal turns it into a
+native notification.
+
+| Protocol | Sequence | Terminals |
+|---|---|---|
+| OSC 777 | `ESC ] 777 ; notify ; title ; body` | Ghostty, WezTerm, Warp, Contour, VTE (GNOME Terminal, Tilix, Terminator), rxvt, Windows Terminal |
+| OSC 9 | `ESC ] 9 ; title: body` | iTerm2, Apple Terminal, ConEmu |
+| bell | `BEL` | everything else |
+
+Detection reads the environment only (`TERM_PROGRAM`, `TERM`, `WT_SESSION`,
+`VTE_VERSION`), so it never blocks and never touches the input stream;
+`protocol` pins it. Inside tmux the sequence is wrapped in DCS passthrough —
+tmux needs `set -g allow-passthrough on` — and inside GNU Screen in a Screen
+DCS. kitty speaks OSC 99 only, which is not implemented, so it keeps the bell;
+install the extra to reach it through the desktop instead.
+
+## Failure is always silent
+
+A missing extra, a desktop without a notification server, a refused write: each
+falls through to the next channel and never raises into the prompt. There is no
+sound, no remote push and no notification when a turn merely ends — only when a
+prompt is waiting for you.