docs: relocate DRIVER-MANAGER-MIGRATION-PLAN to archive + cleanup

The DRIVER-MANAGER-MIGRATION-PLAN was self-declared complete (the
driver-manager cutover happened 2026-07-23 per local/AGENTS.md). It
is now historical reference material rather than current planning
authority. Move it from local/docs/ into the established
legacy-obsolete-2026-07-25/ archive directory, updating every
inbound reference.

Also includes minor cross-doc alignment for the previous round's
relocations:

- local/AGENTS.md: update DRIVER-MANAGER-MIGRATION-PLAN to point to
  the legacy archive
- local/docs/REDBEAR-FULL-SDDM-BRINGUP.md: alignment update
- local/docs/CONSOLE-TO-KDE-DESKTOP-PLAN.md: alignment update
- local/docs/archived/README.md: refresh archive contents note
- local/recipes/system/redbear-driver-policy/source/policy/README.md:
  policy doc drift alignment
- local/scripts/guard-recipes.sh: fix symlink target computation
  (relative path was being glued onto an absolute path, producing
  malformed dangling links like '../..//mnt/.../recipe.toml')
  -- this is a real bug fix discovered during this audit round.

local/scripts/guard-recipes.sh

@@ -73,12 +73,14 @@ case "$MODE" in
         FIXED=0
         find "$LOCAL_RECIPES" -name "recipe.toml" -type f | while read -r local_recipe; do
             rel="${local_recipe#$LOCAL_RECIPES/}"
-            # Compute relative symlink path
-            depth=$(echo "$rel" | tr -cd '/' | wc -c)
-            up=""
-            for ((i=0; i<depth; i++)); do up="../$up"; done
-            target="$up$local_recipe"
             main="$MAIN_RECIPES/${rel%/*}/recipe.toml"
+            # Relative symlink target from the link's directory to the real
+            # recipe under local/recipes/. Computed with realpath so the depth
+            # is always correct. The previous "$up$local_recipe" form glued a
+            # relative prefix onto an ABSOLUTE path (local_recipe comes from
+            # `find "$LOCAL_RECIPES"`, which is absolute), producing malformed
+            # dangling links like "../..//mnt/.../recipe.toml".
+            target="$(realpath -m --relative-to="$(dirname "$main")" "$local_recipe")"
 
             if [ ! -L "$main" ] || [ "$(readlink "$main")" != "$target" ]; then
                 # If the parent directory is a symlink into local/recipes/, the
@@ -148,11 +150,11 @@ case "$MODE" in
         echo "Restoring all symlinks from local/recipes/..."
         find "$LOCAL_RECIPES" -name "recipe.toml" -type f | while read -r local_recipe; do
             rel="${local_recipe#$LOCAL_RECIPES/}"
-            depth=$(echo "$rel" | tr -cd '/' | wc -c)
-            up=""
-            for ((i=0; i<depth; i++)); do up="../$up"; done
-            target="$up$local_recipe"
             main="$MAIN_RECIPES/${rel%/*}/recipe.toml"
+            # See --fix branch above: use realpath so the relative target is
+            # always well-formed (never a relative prefix glued onto an
+            # absolute path).
+            target="$(realpath -m --relative-to="$(dirname "$main")" "$local_recipe")"
 
             mkdir -p "$(dirname "$main")"
             rm -f "$main"