fix(install): make setup failures explicit and atomic

Installer pipelines masked dependency and download failures, causing
false success messages and unsafe config replacement.

Atomic updates and current upstream installers keep failures visible.

install_merlin_worker.sh

@@ -1,10 +1,10 @@
 #!/bin/bash
 
-# Exit on any error
-set -e
+# Exit if either side of a download pipeline fails
+set -euo pipefail
 
 # Download and execute the patch script
-if ! curl -s https://git.miomio.moe/mio/easyzsh/raw/branch/master/patch.sh | bash -s merlin_worker; then
+if ! curl -fsSL https://git.miomio.moe/mio/easyzsh/raw/branch/master/patch.sh | bash -s -- merlin_worker; then
     echo "Error: Failed to download or execute patch script"
     exit 1
 fi
@@ -12,7 +12,7 @@ fi
 # Check if ~/.bashrc exists and contains PYTHONPATH export
 if [ -f "$HOME/.bashrc" ]; then
     # Extract PYTHONPATH from ~/.bashrc (look for export PYTHONPATH=...)
-    BASHRC_PYTHONPATH=$(grep -E "^export PYTHONPATH=" "$HOME/.bashrc" | tail -1)
+    BASHRC_PYTHONPATH=$(grep -E "^export PYTHONPATH=" "$HOME/.bashrc" | tail -1 || true)
     
     if [ -n "$BASHRC_PYTHONPATH" ]; then
         echo "Found PYTHONPATH in ~/.bashrc: $BASHRC_PYTHONPATH"
@@ -46,5 +46,5 @@ if [ -f "$HOME/.bashrc" ]; then
         echo "No PYTHONPATH export found in ~/.bashrc"
     fi
 else
-    echo "~/.bashrc not found"
+    echo "$HOME/.bashrc not found"
 fi