feat(tui): refine session tab activity indicators - #42144

What

Refines session-tab activity feedback in both layouts:

• vertical tabs use a compact 10-cell running sweep instead of washing the full row
• selected shortcuts stay neutral, while running shortcuts turn interactive blue
• start, reprompt, and completion brighten the shortcut, then settle into its durable state
• vertical flashes radiate from the shortcut with a feathered falloff
• top tabs adopt the same shortcut color and flash semantics without changing their background pulse
• the Tabs story can hold runs open, reprompt the selected session, end runs, and switch layouts

How

• packages/tui/src/component/session-tabs.tsx shares a number-ignition primitive across vertical and horizontal tabs and applies the selected/running color semantics.
• packages/tui/src/component/tab-pulse.tsx adds an optional flash tail so localized flashes can fade spatially instead of ending as a hard block.
• packages/tui/src/feature-plugins/system/storybook/ adds reusable footer chrome and richer manual controls for inspecting tab states.

Scope

This does not change the horizontal tab background pulse geometry. It only aligns shortcut color and ignition behavior there.

Testing

• bun typecheck in packages/tui
• bun run test in packages/tui: 689 passed, 5 skipped
• push hook monorepo typecheck: 32 packages passed
• real PTY verification in both left-rail and top-strip layouts

Demo

Real PTY recording with the opencode-drive fixture selected. It shows vertical start/reprompt, then top-tab reprompt/completion.