Move ai-stack and paintplus vendored source under vendor/

Matches the existing vendor/easy-asterisk convention (used by
services/asterisk.sh) instead of two one-off top-level directories that
cluttered the repo root and didn't look like anything else next to
setup.sh, lib/, services/, extras/. Only the two services' own SRC_DIR
path resolution and header comments needed updating — nothing else in
the repo referenced the old ./ai-stack / ./paintplus paths.

Also documents vendor/ in README.md's Layout section.

vendor/ai-stack/systemd/install.sh

@@ -0,0 +1,33 @@
+#!/bin/bash
+# Install all local-ai systemd user units and enable timers
+set -e
+
+UNIT_DIR="$HOME/.config/systemd/user"
+SRC="$(cd "$(dirname "$0")" && pwd)"
+
+mkdir -p "$UNIT_DIR"
+
+for unit in "$SRC"/*.service "$SRC"/*.timer; do
+    name=$(basename "$unit")
+    ln -sf "$unit" "$UNIT_DIR/$name"
+    echo "Linked $name"
+done
+
+systemctl --user daemon-reload
+
+for timer in "$SRC"/*.timer; do
+    name=$(basename "$timer")
+    systemctl --user enable --now "$name"
+    echo "Enabled $name"
+done
+
+echo ""
+systemctl --user list-timers kiwix-update.timer ollama-update.timer
+echo ""
+echo "Run manually:"
+echo "  systemctl --user start kiwix-update.service"
+echo "  systemctl --user start ollama-update.service"
+echo ""
+echo "Logs:"
+echo "  journalctl --user -u kiwix-update.service -f"
+echo "  journalctl --user -u ollama-update.service -f"