fix(agent): resolve reasoningMode from profile config and session meta

- Read reasoningMode from profile config and storedMeta when not
  explicitly set via options (matching thinkingLevel pattern)
- Skip extractThinking() call when reasoningMode is "off"
- Clean up redundant ?? undefined casts in CLI entry points

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/agent/cli/non-interactive.ts

@@ -177,7 +177,7 @@ async function main() {
     baseUrl: opts.baseUrl,
     systemPrompt: opts.system,
     thinkingLevel: opts.thinking as any,
-    reasoningMode: (opts.reasoning as any) ?? undefined,
+    reasoningMode: opts.reasoning as any,
     cwd: opts.cwd,
     sessionId: opts.session,
     debug: opts.debug,