fix(sisyphus-agent): handle OpenCode installer failure with pinned version fallback

Replace retry loop with intelligent fallback strategy:
- Try default installer first (better for version discovery)
- On failure, fallback to pinned version 1.0.204
- Handle corrupted downloads with direct fallback install

This addresses the sisyphus-agent workflow failure where OpenCode's installer failed
with 'Failed to fetch version information' error.

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

.github/workflows/sisyphus-agent.yml

@@ -86,14 +86,19 @@ jobs:
 
           # Install OpenCode (skip if cached)
           if ! command -v opencode &>/dev/null; then
-            for i in 1 2 3; do
-              echo "Attempt $i: Installing OpenCode..."
+            echo "Installing OpenCode..."
             curl -fsSL https://opencode.ai/install -o /tmp/opencode-install.sh
+            
+            # Try default installer first, fallback to pinned version if it fails
             if file /tmp/opencode-install.sh | grep -q "shell script\|text"; then
-                bash /tmp/opencode-install.sh && break
+              if ! bash /tmp/opencode-install.sh 2>&1; then
+                echo "Default installer failed, trying with pinned version..."
+                bash /tmp/opencode-install.sh --version 1.0.204
+              fi
+            else
+              echo "Download corrupted, trying direct install with pinned version..."
+              bash <(curl -fsSL https://opencode.ai/install) --version 1.0.204
             fi
-              echo "Download corrupted, retrying in 5s..."
-            done
           fi
           opencode --version