Let Hyprland --verify-config load the startup cursor setup

Problem

Hyprland --verify-config reports "config ok" for a stock 4.0.6 config. With 4.5.0-rc1 it fails, then the process crashes. Tested with Hyprland 0.56.2 on an Omarchy machine, using a fresh ~/.config copied from config/.

$ HOME=$H XDG_RUNTIME_DIR=$H/run OMARCHY_PATH=$RC Hyprland --verify-config -c $H/.config/hypr/hyprland.lua
ERR ]: Lua error (unknown): .../default/hypr/startup-cursor.lua:78: hl.env: second argument (value) must be a string: string type requires a string
timeout: the monitored command dumped core

There are two causes:

1. The startup-cursor handler passes nil to hl.env (Omarchy; fixed here). default/hypr/startup-cursor.lua:78 passes os.getenv("HYPRLAND_INSTANCE_SIGNATURE") to hl.env. A real compositor always sets that variable before it loads the config (CCompositor::CCompositor, src/Compositor.cpp:208 at v0.56.2). Verification mode returns before that point (:187), so the value is nil there.
2. Hyprland 0.56.2 segfaults when hl.timer runs under --verify-config (upstream). A one-line config reproduces it: hl.timer(function() end, { timeout = 15000, type = "oneshot" }) exits with code 139. The same startup-cursor handler calls hl.timer at line 91.

Fix

The config.reloaded handler now returns early when HYPRLAND_INSTANCE_SIGNATURE is unset. In a running compositor that variable is always set, so a real session behaves exactly as before.

Verify

These checks ran with Hyprland 0.56.2:

• The fresh RC user config: config ok.
• A 4.0.6 user config with the RC defaults (the upgrade case): config ok.
• The RC config with each of the 23 rendered themes: config ok for every one.

test/shell.d/hyprland-startup-cursor-test.sh already sets HYPRLAND_INSTANCE_SIGNATURE, so it is unaffected.

Not fixed here

Hyprland --verify-config run from a terminal inside a Hyprland session inherits the signature. It still reaches hl.timer and segfaults (cause 2). That is hyprwm/Hyprland#16591, "--verify-config segfaults on exit when the Lua config creates an hl.timer". It is closed upstream, so the segfault goes away once Omarchy ships a Hyprland that includes the fix. Nothing to file there.

Duplicate check: no issue or PR in omacom/omarchy for verify-config. The startup-cursor issues #14836, #14969, #16091 and #14512 are about runtime cursor behavior, not this.

Found while testing Omarchy 4.5.0-rc1.