TE-12511: CLI-Capture - Fix 32767px screenshot height limit & per-viewport error isolation

[shrinishLT]

Summary

• 32767px height cap: Pages taller than 32,767px (Safari/Firefox browser engine limit) now gracefully degrade to a viewport-based screenshot capped at 32,767px instead of crashing with Cannot take screenshot larger than 32767 pixels on any dimension
• Per-viewport error isolation: A single viewport/browser screenshot failure no longer aborts remaining captures for that URL. Uses Promise.allSettled for browser-level parallelism and per-viewport try/catch within the loop.
• Aligned with the existing fix in dotlapse-visual-ui-pixel

Files Changed

• src/lib/constants.ts — Added MAXIMUM_POSSIBLE_PAGE_HEIGHT: 32767
• src/lib/screenshot.ts — Added getMaxPageHeight() helper, height cap logic, per-viewport try/catch, Promise.allSettled in async capture

Test plan

• Test smartui capture against a page with height > 32767px on Safari and Firefox — verify capped screenshot is produced with warning log
• Test with Chrome (should not be affected, passes through normally)
• Test with a multi-viewport config where one viewport is intentionally broken — verify remaining viewports still capture
• Test parallel mode (--parallel) with a failing browser — verify other browsers complete
• Verify existing capture flows (normal pages, mobile devices) are unaffected

JIRA: TE-12511

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