Fix overlapping text in responsive window docs

[elithrar]

• Root cause: the Application window example sets a 760px maximum width but shrinks on mobile. Its header forced layout="inline", leaving the description in a column too narrow for its text. Text overlapped the Theme selector and Apply button at 320px and 390px.
• Fix: let that header use the existing automatic container layout. The description stacks above the controls when narrow and stays beside them when space permits. Preserve the stacked window chrome and stacked action row.
• Copy: label fixture widths “Up to …px” and remove the unconditional “above the breakpoint” caption, so the descriptions remain accurate on mobile.
• Regression: extend the existing browser checks to detect rendered description text intersecting the actions, which the previous outer-frame containment checks missed. The new assertions fail on the original example at 320px and 390px.
• Responsive validation: inspect before/after captures at 320, 390, 768, and 1280px; resize mounted examples through 16 additional widths from 360 to 1440px, including breakpoint neighbors. No text/control overlap or document overflow remains.
• Checks: npm run check passes (54 unit tests), all 24 browser tests pass, and library/docs builds pass. Existing menu, select, autocomplete, and overlay geometry regressions pass. Browser validation used Chromium; Safari/WebKit was not separately exercised.

The change is limited to the existing docs example and its browser regressions.