Agentic UI: Add a Learn more modal for publishing and syncing

[shaunandrews]

Related issues

• STU-2162
• Stacked on Agentic UI: Make the site identity a menu with quick actions #4447 (interactive site identity menu).

Stack

• Agentic UI: Replace the site dropdown with a permanent header #4445 — Permanent site header
• Agentic UI: Make the site identity a menu with quick actions #4447 — Interactive site identity menu
• Agentic UI: Add a Learn more modal for publishing and syncing #4448 — Learn more modal (this PR)

⚠️ Visual change: needs human review in light + dark mode.

Repurposed PR: previously "Share dialog", now the Learn-more modal. Preview sharing already ships as the Share menu in #4445, so this PR is just the explanatory modal.

How AI was used in this PR

Wrote the modal copy and wiring, and verified it in the local agentic UI (studio ui).

Proposed Changes

Add a single Learn more modal that explains publishing and syncing, reachable from both the Sync menu and the Publish picker.

• Covers how publishing connects a live WordPress.com/Pressable site, how push/pull sync moves work between local and live, the destination-database-replacement warning, and eligibility.
• One shared InfoDialog primitive backs it, so the modal stays visually consistent.

Additive on top of #4447.

Screenshots

Learn more modal	"Learn more" in the Publish picker

Testing Instructions

1. Open the Publish picker (unconnected site) and click Learn more — the modal opens.
2. Open the Sync menu (connected site) and confirm Learn more opens the same modal.
3. Confirm the copy reads correctly and Got it dismisses it.
4. Check light + dark appearance and the browser console for errors.

Verification completed

• npm run typecheck (clean)
• apps/ui site-toolbar unit tests pass

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[shaunandrews]

🤖 AI-written review note — verified against the current PR head.

Share remains enabled while Push/Pull is running and preview publishing reports into the same per-site sync-activity entry. In the cumulative stack, #4451 also gives preview and sync the same sync-${siteId} toast ID. Concurrent Share + Push/Pull can therefore overwrite each other’s activity/toast state and may operate on the same local site simultaneously. Please coordinate or uniquely identify these operations.

[shaunandrews]

Superseded by the re-split STU-2162 stack, rebuilt on current trunk with clearer branch names and standalone-reviewable slices: #4611 → #4612 → #4613 → #4614 → #4615 → #4616. Closing to avoid the stale branch names here.