fix: comprehensive boot warnings and exceptions — fixable silenced, unfixable diagnosed

Build system (5 gaps hardened):
- COOKBOOK_OFFLINE defaults to true (fork-mode)
- normalize_patch handles diff -ruN format
- New 'repo validate-patches' command (25/25 relibc patches)
- 14 patched Qt/Wayland/display recipes added to protected list
- relibc archive regenerated with current patch chain

Boot fixes (fixable):
- Full ISO EFI partition: 16 MiB → 1 MiB (matches mini, BIOS hardcoded 2 MiB offset)
- D-Bus system bus: absolute /usr/bin/dbus-daemon path (was skipped)
- redbear-sessiond: absolute /usr/bin/redbear-sessiond path (was skipped)
- daemon framework: silenced spurious INIT_NOTIFY warnings for oneshot_async services (P0-daemon-silence-init-notify.patch)
- udev-shim: demoted INIT_NOTIFY warning to INFO (expected for oneshot_async)
- relibc: comprehensive named semaphores (sem_open/close/unlink) replacing upstream todo!() stubs
- greeterd: Wayland socket timeout 15s → 30s (compositor DRM wait)
- greeter-ui: built and linked (header guard unification, sem_compat stubs removed)
- mc: un-ignored in both configs, fixed glib/libiconv/pcre2 transitive deps
- greeter config: removed stale keymapd dependency from display/greeter services
- prefix toolchain: relibc headers synced, _RELIBC_STDLIB_H guard unified

Unfixable (diagnosed, upstream):
- i2c-hidd: abort on no-I2C-hardware (QEMU) — process::exit → relibc abort
- kded6/greeter-ui: page fault 0x8 — Qt library null deref
- Thread panics fd != -1 — Rust std library on Redox
- DHCP timeout / eth0 MAC — QEMU user-mode networking
- hwrngd/thermald — no hardware RNG/thermal in VM
- live preload allocation — BIOS memory fragmentation, continues on demand

local/recipes/qt/qtwayland/source/examples/wayland/spanning-screens/doc/src/spanning-screens.qdoc

@@ -0,0 +1,60 @@
+// Copyright (C) 2021 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+ * \title Spanning Screens
+ * \example spanning-screens
+ * \examplecategory {Embedded}
+ * \brief Spanning Screens is an example that demonstrates how to let Wayland clients span multiple screens.
+ * \ingroup qtwaylandcompositor-examples
+ *
+ * \section1 Introduction
+ *
+ * Spanning screens is a Wayland compositor example that maximizes clients across a top and a bottom
+ * screen.
+ *
+ * \image spanning-screens.jpg
+ *
+ * For an introduction to the basic principles of creating a \l{Qt Wayland Compositor} with Qt,
+ * see the \l{Minimal QML}{Minimal QML example}.
+ *
+ * \section1 Supporting Multiple Screens
+ *
+ * In \l{Qt Wayland Compositor} a screen is represented by a \l{WaylandOutput}, and a \l Window is
+ * used to contain the \l{Qt Quick} scene representing both clients and the compositor's UI.
+ *
+ * In this example, a multi-screen setup is emulated by creating two windows on the primary screen,
+ * but the code can easily be modified to target multiple physical screens.
+ *
+ * \snippet spanning-screens/main.qml enable screens
+ *
+ * Since each \l Window represents an isolated \l{Qt Quick} scene, this means we need a trick to
+ * have the same client content display inside both windows. The way to do this in
+ * \l{Qt Wayland Compositor} is to create two views of the same client content: One for the "top"
+ * window and one for the "bottom". The views share a reference to the same underlying graphics buffer.
+ * This allows us to copy different areas of the client's surface onto each of the windows.
+ *
+ * \snippet spanning-screens/main.qml create items
+ *
+ * When the client connects to the \l{Shell Extensions - Qt Wayland Compositor}{shell extension}
+ * \l{XdgShell}, we create two references to the surface. One of them is added to the "top" output,
+ * and the second to the "bottom". The item on the bottom output also gets an offset corresponding
+ * to the height of the top output. This ensures that the part of the client surface showing on
+ * the bottom output starts where the top output ends.
+ *
+ * \snippet spanning-screens/main.qml size
+ *
+ * In addition, we tell the client to resize its surface so that it fills both the top and bottom
+ * window. The end result is a client that spans two windows, or "screens".
+ *
+ * Referencing the same client surface from multiple items is a tool which can be used for many
+ * things. For a demonstration of a desktop-style compositor where windows can be moved from screen
+ * to screen, take a look at the \l{Multi Screen}{Multi Screen example}.
+ *
+ * The \l{Multi Output}{Multi Output example} shows how client surfaces can be displayed on multiple
+ * outputs with different sizes and other properties.
+ *
+ * \note In order to support multiple Wayland outputs in the same compositor, the
+ * \l Qt::AA_ShareOpenGLContexts attribute must be set before the \l QGuiApplication
+ * object is constructed.
+ */