Dim and sleep locked displays after inactivity

Add adjustable lock-only inactivity delays, a smooth dimming fade and DRM display sleep without changing output layout. Input, session resume and policy changes wake displays. Pending flips retire before power-off, and protected fallback frames preserve the policy after an early locker crash while unlock ownership checks remain strict.

Reduce the password field and avatar, expose delays in Settings, document the practical swaylock comparison and remove the completed backlog.

Validation: independent review cleared; 255 compositor tests, 7 locker tests and 15 Settings tests pass; affected debug binaries rebuilt. Isolated visual smoke remains blocked by an unlocked nested screenshot timeout, matching the previously established baseline presentation limitation. Real DRM display sleep requires a live session check.

docs/locking.md

@@ -15,7 +15,7 @@ This is an ordinary, closable window. Submitting the field does not call PAM,
 lock, or unlock anything. Do not type your actual password into a visual preview.
 
 Settings → Lock screen provides clock visibility, date visibility, time format,
-wallpaper dimming and softness, and a safe preview button. Your account picture is loaded from
+wallpaper dimming and softness, inactivity delays, and a safe preview button. Your account picture is loaded from
 AccountsService or `~/.face`, with a user silhouette as a fallback.
 
 The locker reads Ferese's wallpaper, theme colors, typography, and shell radius
@@ -64,3 +64,46 @@ never reports success merely because the window appeared.
 Validation references: [session-lock protocol](https://wayland.app/protocols/ext-session-lock-v1),
 [PAM authentication](https://man7.org/linux/man-pages/man3/pam_authenticate.3.html),
 and [PAM account checks](https://man7.org/linux/man-pages/man3/pam_acct_mgmt.3.html).
+
+## Inactivity and display sleep
+
+A locked display dims after 30 seconds without input and sleeps after 120 seconds.
+Dimming fades over half a second. Any keyboard, pointer or touch activity restores
+brightness and wakes the display while keeping the session locked. The compositor
+owns this policy, so it remains effective if the locker crashes. Sleep starts only
+after the compositor has confirmed that every display is protected.
+
+Settings → Lock screen adjusts both delays. Zero disables that action:
+
+```kdl
+lock-screen {
+    dim-after-seconds 30
+    sleep-after-seconds 120
+}
+```
+
+These delays are independent of automatic locking. Existing idle inhibitors from
+apps cannot keep an already locked display awake. In a direct session, display
+sleep uses DRM DPMS without removing outputs or rearranging workspaces; nested
+previews show black instead of powering off the host display. This puts displays
+to sleep, not the computer. Suspend remains a separate system power action.
+
+## Practical swaylock comparison
+
+| Behavior | Ferese Lock |
+| --- | --- |
+| Secure Wayland locking and protection after a locker crash | Session-lock protocol, compositor-owned fallback |
+| All displays, including hotplug | Separate lock surface for each display |
+| Readiness before an idle manager permits suspend | Default command waits for compositor confirmation |
+| Password verification | PAM authentication and account checks on a worker |
+| Password clearing and Caps Lock feedback | Escape clears; Caps Lock indicator |
+| Authentication failure feedback and retry delay | Error message and bounded retry delay |
+| Wallpaper, font and color customization | Shared Ferese theme and Settings |
+| Inactivity and display power | Compositor dimming and DPMS; input restores brightness |
+
+[Swaylock](https://github.com/swaywm/swaylock/blob/master/swaylock.1.scd) provides
+additional appearance flags, layout indicators and readiness-FD CLI options.
+Ferese uses its shared configuration and existing startup acknowledgement instead.
+Like the [swayidle example](https://github.com/swaywm/swayidle/blob/master/swayidle.1.scd),
+locking and display sleep are separate from system suspend. Password changes and
+interactive multi-factor prompts remain outside this password-only interface.