feat(layout): add window-layout shell + /consume, /discover, /create
Introduces the Morgenblau Window-framed authenticated shell distinct
from the starter-pack sidebar. Top chrome carries the three section
tabs and right-aligned add-source / profile / settings icon buttons;
the Window is the only scroll surface so the page itself never moves.
Wires the three new Inertia pages through app.tsx's layout switch and
adds matching auth-protected routes. Footer stamp uses Caveat secondary
at the new text-2xs token.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>