fix(installer): chown target files by numeric id, not live-medium name

The end-4 step's chowns ran on the live medium, whose /etc/passwd has
no $USERNAME (the user exists only inside /mnt), so 'chown -R
alvin:alvin' failed with "invalid user" and the ERR trap aborted the
install at line 543. Resolve uid/gid once via arch-chroot id and chown
by number; the three remaining name-based chowns (fork/fish/hypr
restores) would have hit the same wall later.

Replace those three mid-function chowns with one catch-all over the
target home after the last root-side write: sed -i on the presets
rewrites through a temp file, which leaves them root-owned with no
chown after it.

systemctl --user enable ydotool.service could never work inside the
chroot (no /run/user/UID/bus exists before boot; it only ever warned
with "Failed to connect to user scope bus", so ydotool never
autostarted). Write the symlink enable would write:
~/.config/systemd/user/default.target.wants/ydotool.service ->
/usr/lib/systemd/user/ydotool.service.

airootfs/usr/local/bin/alvin-install

@@ -539,8 +539,15 @@ install_end4_dots() {
     local dots_ok=true
     local setups_done=true
 
+    # These chowns run on the live medium, whose /etc/passwd has no
+    # $USERNAME — the user exists only inside $TARGET — so name lookup fails
+    # ("chown: invalid user"). Resolve the numeric ids from the target and
+    # chown by number; the catch-all at the end of this function does the same.
+    local owner
+    owner="$(arch-chroot "$TARGET" id -u "$USERNAME"):$(arch-chroot "$TARGET" id -g "$USERNAME")"
+
     cp -a /opt/dots-hyprland "$repo_on_host"
-    chown -R "${USERNAME}:${USERNAME}" "$repo_on_host"
+    chown -R "$owner" "$repo_on_host"
 
     echo "${USERNAME} ALL=(ALL) NOPASSWD:ALL" > "${TARGET}/etc/sudoers.d/99-end4-install"
     chmod 440 "${TARGET}/etc/sudoers.d/99-end4-install"
@@ -597,10 +604,18 @@ install_end4_dots() {
         arch-chroot "$TARGET" systemctl enable bluetooth.service >>"$LOG" 2>&1 \
             || warn "Could not enable bluetooth.service (see $LOG)."
     fi
+    # `systemctl --user` cannot work in this chroot either: it needs
+    # /run/user/UID/bus, which does not exist until the target boots (it only
+    # ever reports "Failed to connect to user scope bus"). Write the symlink
+    # `enable` would write — the same absolute link systemctl produces.
     if [[ -f "${TARGET}/usr/lib/systemd/user/ydotool.service" ]]; then
-        arch-chroot "$TARGET" runuser -u "$USERNAME" -- env HOME="$home_in_target" \
+        local yd_wants="${TARGET}${home_in_target}/.config/systemd/user/default.target.wants"
-            systemctl --user enable ydotool.service >>"$LOG" 2>&1 \
+        if mkdir -p "$yd_wants" \
-            || warn "Could not enable ydotool.service for ${USERNAME} (see $LOG)."
+            && ln -sfn /usr/lib/systemd/user/ydotool.service "$yd_wants/ydotool.service"; then
+            log "ydotool.service enabled for ${USERNAME} (symlinked in user unit dir)."
+        else
+            warn "Could not enable ydotool.service for ${USERNAME} (see $LOG)."
+        fi
     fi
 
     # Everything end-4 answered "i" to. systemctl/gsettings are the lines known
@@ -640,7 +655,6 @@ install_end4_dots() {
         mkdir -p "$(dirname "$fork_dst")"
         rm -rf "$fork_dst"
         cp -a "$fork_src" "$fork_dst"
-        chown -R "${USERNAME}:${USERNAME}" "$fork_dst"
     fi
 
     # Same for fish: end-4 syncs ~/.config/fish with rsync --delete, keeping
@@ -659,7 +673,6 @@ install_end4_dots() {
             grep -qF "alias q 'qs -c end4-pC'" "${fish_dst}/config.fish" \
                 || warn "fish 'q' alias still points at the upstream ii config (see $LOG)."
         fi
-        chown -R "${USERNAME}:${USERNAME}" "$fish_dst"
     fi
 
     local configs_ok=true
@@ -681,7 +694,6 @@ install_end4_dots() {
 
     if [[ -d /etc/skel/.config/hypr/custom ]]; then
         cp -rfT /etc/skel/.config/hypr/custom "${TARGET}${home_in_target}/.config/hypr/custom"
-        chown -R "${USERNAME}:${USERNAME}" "${TARGET}${home_in_target}/.config/hypr/custom"
     fi
 
     # Presets ship with absolute paths from the build machine; repoint them at
@@ -693,6 +705,12 @@ install_end4_dots() {
         sed -i "s|/home/alvin/|/home/${USERNAME}/|g" "$preset"
     done
 
+    # Everything above that ran as root from the live medium (repo copy,
+    # fork/fish/hypr restores, and the presets sed -i just rewrote through a
+    # temp file) left root-owned files in the home — one pass fixes them all.
+    # Numeric ids again: this chown also runs on the medium, not in the chroot.
+    chown -R "$owner" "${TARGET}${home_in_target}"
+
     if $dots_ok && $configs_ok; then
         log "end-4 dotfiles installed for ${USERNAME} (setups_done=${setups_done} skipped=${#ignored[@]})."
         ok "end-4 dotfiles installed."