Compose and verify the Tideline shell as one coherent running TUI

[Hmbown]

Problem

The redesign currently exists as isolated source slices: current startup mark, clean-launch routing, composer enclosure, quiet boot diagnostics, interactive route control, and active Tideline rail. A green isolated slice does not prove the actual binary composes those pieces into the approved product experience.

Scope

Create one integration lane from current main that composes the reviewed slices without reviving the retired fluke mark or creating a second route/runtime authority. Use the approved diving-whale/current mark whose wave forms the prompt symbol.

Acceptance

• Clean startup after the explicit onboarding path shows the approved Startup Hero, current mark, useful first moves, and pre-session composer.
• Active sessions show the responsive Tideline rail at the documented 100/120-column breakpoints, quiet boot diagnostics, truthful route entry point, and a rounded composer that uses one measured input rect for wrapping, cursor, and hit testing.
• 80, 100, and 120-column PTY frames cover clean/startup and active states and are compared to the approved Tideline references.
• Existing source PRs feat(tui): restore approved current startup mark #5753, fix(tui): restore rounded active composer enclosure #5758, fix(tui): keep MCP boot detail out of chat #5760, fix(tui): retain startup hero on clean launch #5762, fix(tui): make topbar route segment interactive #5763, and fix(tui): render truthful active Tideline rail #5765 are either composed faithfully or their replacement is named with a reason.
• Provider catalog/readiness/runtime authority remains separate under Unify provider route authority across picker, readiness, runtime, API, and CLI #5755; this issue must not claim it is fixed by chrome changes.
• No merge, tag, deploy, or release follows without the applicable review and founder gates.