Fix SDK path: add settingSources and default system prompt (#726)

Two fixes for the Agent SDK path (USE_AGENT_SDK=true):

1. Add settingSources to load filesystem settings
   - Without this, CLI-installed plugins aren't available to the SDK
   - Also needed to load CLAUDE.md files from the project

2. Default systemPrompt to claude_code preset
   - Without an explicit systemPrompt, the SDK would use no system prompt
   - Now defaults to { type: "preset", preset: "claude_code" } to match CLI behavior

Also adds logging of SDK options (excluding env) for debugging.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

base-action/src/run-claude-sdk.ts

@@ -75,6 +75,9 @@ export async function runClaudeWithSdk(
   }
 
   console.log(`Running Claude with prompt from file: ${promptPath}`);
+  // Log SDK options without env (which could contain sensitive data)
+  const { env, ...optionsToLog } = sdkOptions;
+  console.log("SDK options:", JSON.stringify(optionsToLog, null, 2));
 
   const messages: SDKMessage[] = [];
   let resultMessage: SDKResultMessage | undefined;