feat(tui): add display-level toggles to collapse/hide thinking and tool-call details

[Chekhovin]

Summary

Add display-layer options to control how much detail the TUI shows for
thinking blocks and tool calls — e.g. show only a "Thinking…" placeholder or
a one-line "Running tool: Read" summary instead of the full content.

Motivation

Thinking blocks and tool-call details can dominate the scrollback, especially
with high reasoning effort or MCP-heavy sessions. Users who trust the agent's
process and only care about final replies currently have no way to reduce
this visual noise.

The existing controls do not cover this:

• [thinking] enabled = false and the "Toggle thinking mode" switch change
  model behavior (reasoning on/off), not display.
• Thinking blocks can be collapsed manually, but only per-block and not
  persistently.
• There is no option at all for tool-call rendering.

The request is purely presentational: the model still thinks and calls tools
exactly as before; the TUI just renders less.

Proposed solution

New optional fields in tui.toml:

[display]
# "full" (default, current behavior) | "collapsed" (folded by default,
# expandable on demand) | "placeholder" (single "Thinking…" line, not expandable)
thinking = "collapsed"

# "full" (default) | "summary" (one line per call: tool name + key arg +
# status) | "hidden"
tool_calls = "summary"

Behavior notes:

• collapsed should be expandable via the existing fold interaction, so
  details remain one keystroke away.
• placeholder / hidden only affects rendering; content is still recorded
  in the session transcript for later inspection.
• Errors and permission prompts must always render in full regardless of
  these settings (hiding a failure or an approval request would be a
  footgun).

Alternatives considered

• [thinking] effort = "low" — shortens thinking but still displays it, and
  changes model behavior.
• Disabling thinking entirely — loses the reasoning quality.

Environment

kimi-code 0.31.0, Linux (WSL2)