Fix agent install/uninstall sudo placement, add dependency install hints

curl ... | API_URL=... bash runs as the invoking user, not root, so
"sudo" has to go right after the pipe (elevating bash) rather than
before curl — the old commands in the app UI, README, and scripts'
own usage comments put it in a spot that still failed the root check.
Also have install.sh/report-tasks.sh suggest the right package-manager
command (apt/dnf/yum/apk/pacman/zypper) when curl or jq is missing
instead of just failing, and bring the README up to date with both.

agent/linux/uninstall.sh

@@ -2,8 +2,9 @@
 # Removes the Schedule Task Manager agent from this server: stops and deletes
 # its systemd timer/service, the installed script, and its credentials file.
 #
-# Usage:
-#   curl -fsSL https://schedule.example.lan/agent/linux/uninstall.sh | bash
+# Usage (must run as root — if not already root, put sudo right after the
+# pipe so it applies to bash, not to curl):
+#   curl -fsSL https://schedule.example.lan/agent/linux/uninstall.sh | sudo bash
 #
 set -euo pipefail
 
@@ -13,6 +14,8 @@ SYSTEMD_DIR="/etc/systemd/system"
 
 if [[ "$EUID" -ne 0 ]]; then
   echo "This uninstaller must be run as root." >&2
+  echo "If you're piping from curl, put sudo right after the pipe so it elevates bash, not curl:" >&2
+  echo "  curl -fsSL ... | sudo bash" >&2
   exit 1
 fi