Refine Kandelo browser demo dock UI

[brandonpayton]

Summary

• Reworks the Kandelo browser demo around a Playground-inspired dock with floating, full-width, collapsible, movable, and popover behaviors.
• Moves view-specific controls into the dock, adds theme selection/defaults, floating download toasts, Kandelo favicon, and a table-based gallery.
• Tightens demo surfaces: terminal reserved space and focus behavior, framebuffer/modeset sizing, title-bar removal, guide/internals popovers, and browser reload affordances.

Contract scope

• Browser demo presentation and user interaction only.
• Demos continue to consume Kandelo through KernelHost, VFS, PTY, framebuffer, and runtime paths.
• No ABI, kernel, package artifact, or VFS image contract changes intended.

Validation

• Ran: bash scripts/dev-shell.sh bash -lc 'cd apps/browser-demos && npm run build'
• Manually verified with Chrome DevTools during the UI pass: dock collapse/full-width/move behavior, terminal strip focus, theme defaults, guide/internals popover dismissal, gallery URL copy affordance, and modeset/framebuffer fitting.

Not run

• Full Playwright browser suite.
• Kernel, ABI, libc, POSIX, Sortix, and package validation suites, because this PR is scoped to browser demo UI.

[github-actions]

prepare-merge: runtime/materialization tests passed against the synthetic PR merge; package staging and durable package publishing were skipped. merge-gate=success posted on PR HEAD and squash auto-merge enabled.

[github-actions]

prepare-merge: runtime/materialization tests passed against the synthetic PR merge; package staging and durable package publishing were skipped. merge-gate=success posted on PR HEAD and squash auto-merge enabled.