[Atomic 14] Add TerminalStackTrace component with foldable frames

[clawgreen]

Goal

Create a dedicated stack trace component for error output.

Why

Raw stack traces are noisy; foldable frames improve debugging UX.

Scope (atomic)

• New TerminalStackTrace component.
• Toggle collapse/expand.
• Optional frame filtering (e.g., hide node_modules by default).

Acceptance Criteria

• Works with plain string stack traces.
• Keyboard and screen-reader friendly toggles.
• Theme-consistent error styling.

[clawgreen]

Recommended Execution\n- Order: 14 / 17\n- Keep this PR atomic (single-purpose; avoid cross-issue scope).\n- Target PR size: ~50-200 LOC when possible.\n- Dependency: #13.\n- Suggested branch pattern: codex/atomic-14-....