fix(showcase): stretch Command Center's flex-column children to full width (#2631)

The 3-up chart band (cc_rowA/cc_rowB) rendered at a collapsed ~100px width
per column, wide enough to render but far too narrow to be readable — the
"D" chart-width finding from #2616/#2620, not actually fixed by
objectui#2254 despite that PR touching this exact area.

Root cause: cc_root (the page's outer `type:'flex'` container) never set
`alignItems`, so the `flex` component's own default (`align: 'start'` →
Tailwind `items-start`) applied. In a `flex-direction:column` container,
`align-items:flex-start` means children size to their own content instead
of stretching to the container's width — so each grid-based chart band
(cc_rowA/cc_rowB) shrank to whatever intrinsic width its charts naturally
wanted (~100-130px each) rather than filling the ~1100px available.

Verified live (Playwright + a real backend): row-A chart SVGs measured
100px wide before this fix, 350px after — filling the actual available
width. Screenshot-confirmed all three charts now render full width with
readable axes/legends.

The unrelated `coverage.test.ts` failure on this branch (new registry
kinds `trigger`/`router`/`function`/`service` not yet in KIND_COVERAGE)
pre-exists on main and is untouched by this change.

Co-authored-by: Claude <noreply@anthropic.com>

Author: os-zhuang

examples/app-showcase/src/ui/pages/command-center.page.ts

@@ -115,7 +115,7 @@ export const CommandCenterPage = definePage({
           type: 'flex',
           responsiveStyles: {
             large: {
-              minHeight: '100%', display: 'flex', flexDirection: 'column', gap: '16px',
+              minHeight: '100%', display: 'flex', flexDirection: 'column', alignItems: 'stretch', gap: '16px',
               padding: '22px 26px 32px',
               background:
                 'radial-gradient(1200px 540px at 50% -14%, hsl(192 86% 46% / 0.10) 0%, transparent 60%), ' +