docs(plan): render-goal — MissionBanner, needs_human sidebar, MetricSparkline, metric history

[lsm]

Plan document for the Render Goal feature.

Covers four focused tasks:

• MissionBanner component in ChatContainer showing active mission context for room sessions
• RoomContextPanel extended to show needs_human goals alongside active goals
• MetricSparkline pure-SVG component for metric history trend lines
• goal.getMetricHistory daemon RPC handler + frontend wiring + sparkline integration in GoalsEditor