agent: Add reasoning token support for OpenAI reasoning models

- Extract and display reasoning tokens from both Chat Completions and Responses APIs
- Add smart preflight detection to check reasoning support per model/API (cached per agent)
- Support both reasoning_text (o1/o3) and summary_text (gpt-5) formats
- Display reasoning tokens with ⚡ symbol in console and TUI renderers
- Only send reasoning parameters to models that support them
- Fix event type from "thinking" to "reasoning" for consistency

Note: Chat Completions API only returns reasoning token counts, not content (by design).
Only Responses API exposes actual thinking/reasoning events.

todos/todos.md

@@ -1,3 +1,4 @@
+- agent: token usage gets overwritten with each message that has usage data. however, if the latest data doesn't have a specific usage field, we record undefined i think? also,   {"type":"token_usage" "inputTokens":240,"outputTokens":35,"totalTokens":275,"cacheReadTokens":0,"cacheWriteTokens":0} doesn't contain reasoningToken? do we lack initialization?
 - pods: if a pod is down and i run `pi list`, verifying processes says All processes verified. But that can't be true, as we can no longer SSH into the pod to check.
 - agent: start a new agent session. when i press CTRL+C, "Press Ctrl+C again to exit" appears above the text editor followed by an empty line. After about 1 second, the empty line disappears. We should either not show the empty line, or always show the empty line. Maybe Ctrl+C info should be displayed below the text editor.
 - tui: npx tsx test/demo.ts, using /exit or pressing CTRL+C does not work to exit the demo.