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/interactive.ts

@@ -349,7 +349,7 @@ class InteractiveCLI {
       model: this.opts.model,
       systemPrompt: this.opts.system,
       thinkingLevel: this.opts.thinking as AgentOptions["thinkingLevel"],
-      reasoningMode: (this.opts.reasoning as AgentOptions["reasoningMode"]) ?? undefined,
+      reasoningMode: this.opts.reasoning as AgentOptions["reasoningMode"],
       cwd: this.opts.cwd,
       sessionId,
     });