[Atomic 08] Add TerminalLogLine primitive for structured log rows

[clawgreen]

Goal

Create a TerminalLogLine component as the core primitive for structured log display.

Why

TerminalLog currently accepts strings only; structured rows enable better scanning and tooling.

Scope (atomic)

• New component with typed props + JSDoc.
• Support level, timestamp, source, and message.
• Theme-aware level coloring.
• Export from components/terminal.tsx.

Suggested Props

• message: ReactNode
• level?: 'debug' | 'info' | 'warn' | 'error' | 'success'
• timestamp?: string
• source?: string

Acceptance Criteria

• Component renders cleanly in monospace layout.
• Color and spacing are consistent with existing terminal components.
• Playground demo included.

[clawgreen]

Recommended Execution\n- Order: 8 / 17\n- Keep this PR atomic (single-purpose; avoid cross-issue scope).\n- Target PR size: ~50-200 LOC when possible.\n- Dependency: #7.\n- Suggested branch pattern: codex/atomic-8-....