v0.5.3: fix installer require_tty before tee redirect

QEMU boot test of v0.5.2 found service still status=1/FAILURE despite
file present at /usr/local/bin/veilor-installer. Root cause via
`bash -x`: `exec > >(tee -a "$LOG") 2>&1` ran BEFORE require_tty
check; process substitution replaces fd1 with a pipe, so [[ -t 1 ]]
returns false → require_tty bails out with [ERR] message.

Order was self-inflicted bug from v0.5.0. Fix: move require_tty
function definition + call BEFORE the tee redirect. Drop the
redundant require_tty call in the entry block (would fail post-redirect).

overlay/usr/local/bin/veilor-installer

@@ -18,6 +18,18 @@
 set -uo pipefail
 export TERM="${TERM:-linux}"
 LOG=/var/log/veilor-installer.log
+
+# require_tty MUST run before the tee redirect — process substitution
+# replaces fd1 with a pipe, breaking `[[ -t 1 ]]`.
+require_tty() {
+    if ! [[ -t 0 && -t 1 ]]; then
+        echo "[ERR] veilor-installer must run on a real tty" >&2
+        exit 1
+    fi
+}
+require_tty
+
+# Now safe to tee output for log persistence — tty detection already passed.
 exec > >(tee -a "$LOG") 2>&1
 
 # ── Branded styling for gum ─────────────────────────────────────────────
@@ -64,13 +76,6 @@ EOF
     fi
 }
 
-require_tty() {
-    if ! [[ -t 0 && -t 1 ]]; then
-        echo "[ERR] veilor-installer must run on a real tty" >&2
-        exit 1
-    fi
-}
-
 # ── TUI wrapper functions ───────────────────────────────────────────────
 # Each prompt_* call abstracts gum / whiptail. Always emit the chosen value
 # on stdout; non-zero exit on cancel/ESC. Callers use `||` to propagate.
@@ -562,7 +567,7 @@ launch_desktop() {
 }
 
 # ── Entry ──
-require_tty
+# (require_tty already called above before exec redirect — see top of file)
 banner
 
 while true; do