sddm: C-7 migration of 19 sed chains to external patch + cookbook_apply_patches

Migrated sddm (the last lint-recipe erroring
recipe) to use the cookbook_apply_patches helper.
The 19 inline `sed -i` chains in sddm's
[build].script have been captured in
`local/patches/sddm/01-initial-migration.patch`
(122 lines) and replaced with a single
`cookbook_apply_patches "${REDBEAR_PATCHES_DIR}"`
call.

sddm is git-sourced (not tar-sourced), so the
migration script had to:
  1. Snapshot the upstream `source/` dir to
     `source-pristine/` (the migration script
     supports both tar and git sources by using
     whatever's in `source/` as the upstream state).
  2. Apply all 19 sed chains directly to `source/`.
  3. Diff pristine vs post-sed.
  4. Save the diff as the migration patch.

The patch covers 19 sed chains targeting:
  - 6 single-line edits to CMakeLists.txt (XCB,
    XKB, LIBXAU pkg_check, Qt5/Qt6 find_package,
    add_subdirectory(test) removal, enable_testing)
  - 6 `find -exec` patterns for LIBXCB/LIBXKB/
    LIBXAU include-dir stripping across the source
  - 1 LIBJOURNALD QUIET pattern
  - 1 XAuth.cpp removal
  - 1 LIBXAU_LINK_LIBRARIES stripping
  - 1 ioctl(TIOCSCTTY) → ioctl(TIOCSCTTY, NULL) fix
  - 1 XAuth::writeCookieToFile → true
  - 1 #include "XAuth.h" removal
  - 1 LibJournald QUIET

End-to-end verified:
  `make lint-recipe`: 173/173 recipes clean (was
  1 error before this commit). 0 errors.
  `make lint-build-system-all`: passes.

Recipe edit script `edit-kf6-recipes-for-patches.sh`
and migration script `migrate-kf6-seds-direct.sh`
both got a one-line addition for sddm.

lint-recipe summary (final, this commit):
  173/173 clean, 0 errors, 0 warnings (other than
  the 1 pre-existing warning).

local/scripts/edit-kf6-recipes-for-patches.sh

@@ -53,6 +53,7 @@ recipe_dirs=(
     "local/recipes/kde/kglobalacceld"
     "local/recipes/kde/kirigami"
     "local/recipes/kde/konsole"
+    "local/recipes/kde/sddm"
     "local/recipes/kde/kwin"
     "local/recipes/kde/plasma-desktop"
     "local/recipes/kde/plasma-workspace"

local/scripts/migrate-kf6-seds-direct.sh

@@ -47,6 +47,7 @@ recipe_dirs=(
     "local/recipes/kde/kf6-solid"
     "local/recipes/kde/kf6-sonnet"
     "local/recipes/kde/kf6-syntaxhighlighting"
+    "local/recipes/kde/sddm"
     # 7 unclassified (git-sourced or kde/plasma). Their
     # pristine state was snapshotted after a successful
     # `repo fetch`. If the pristine doesn't exist, the