fix(pulse): create ~/Library/LaunchAgents before writing launchd plist

[stevetr68]

Problem

PULSE/manage.sh install writes the launchd plist to $HOME/Library/LaunchAgents/:

PLIST_DST="$HOME/Library/LaunchAgents/$PLIST_NAME.plist"
...
sed -e "s|__HOME__|$HOME|g" -e "s|__BUN_PATH__|$BUN_PATH|g" "$PLIST_SRC" > "$PLIST_DST"

…but the install) case only creates state/ and logs/:

mkdir -p "$PULSE_DIR/state" "$PULSE_DIR/logs"

On a fresh macOS user account, ~/Library/LaunchAgents/ does not exist until something
creates it. When it's missing, the > "$PLIST_DST" redirect fails with
No such file or directory, the install aborts, and the user sees a confusing
port 31337 did not bind error with no obvious cause.

Fix

Add "$HOME/Library/LaunchAgents" to the existing mkdir -p. One-line, idempotent,
no behavior change on accounts where the directory already exists.

-    mkdir -p "$PULSE_DIR/state" "$PULSE_DIR/logs"
+    mkdir -p "$PULSE_DIR/state" "$PULSE_DIR/logs" "$HOME/Library/LaunchAgents"

Hit this on a fresh-account PAI 5 install; this exact patch has been running locally
since. Related to the opaque-install-failure reports.