Fix archive confirmation counts and compact dialog spacing

[ymichael]

Human comments

What was wrong

Archive confirmation reused deletion's direct-child count, including already archived children and missing deeper descendants. A parent whose only child was already archived incorrectly prompted to archive two threads. The shared DialogFooter also supplied horizontal desktop spacing but no spacing between stacked mobile buttons. Related: #3399.

What changed

Archive preview now counts unarchived, non-deleted descendants using the same traversal as archive-all, including live descendants below archived intermediaries and deduplicating hierarchy, lifecycle-owner, and hidden source-fork relationships. Deletion retains its direct non-deleted count. The existing SDK childSummary response exposes unarchivedDescendantCount; CLI/SDK archive operations remain non-interactive. Plugin SDK is bumped to 0.5.30 for its updated bundled response types, and the plugin registry dialog copy is regenerated. Shared dialog footers use an 8px gap at both compact and desktop widths. No daemon wire changes.

How you verified

• 38 focused app tests: archived-only children skip confirmation, mixed archived/live counts, cancellation, Undo, and responsive drawer behavior.
• 22 public parenting route tests: archived/deleted/hidden/unrelated rows, nested descendants, archived intermediaries, duplicate edges, and preview count matching the eventual archive result.
• Turbo typechecks passed for app, server, demo-server, and shared-ui.
• Live Chromium mobile/desktop interaction checks and iOS Simulator Safari layout inspection. Native Safari WebDriver taps did not activate the menu; Safari rendering was inspected after programmatic activation.
• Final commit 50a71995fa: all 16 active CI checks passed; iOS simulator flows and Node Compatibility Smoke were skipped.
• Comparable base/head production builds reproduce and verify both defects at 390/640/1280px. Delete confirmation reproduces the same shared spacing bug. Prepared review fixtures and before/after screenshots are kept in BB thread storage; the persistent review server is rebuilt at the exact final PR head.

AGENT GENERATED