fix(editor): polish context menus and data tokens

[DavidBabinec]

Summary

• improve clearable segmented controls and remove duplicate viewport/context labels
• replace the Content slash menu's one-off styling with the shared context-menu primitive
• extract a reusable data-binding picker shared by Site and Content
• make Content token insertion browse real system, collection, custom media, and repeater fields
• suppress the insert-token tooltip while its picker is open and remove duplicate repeater labels

Why

Several small editor details duplicated labels or used one-off UI. Content token insertion also hardcoded {currentEntry.title} instead of letting users choose from the data available in the current workspace.

Impact

The editor now presents cleaner context controls and one consistent menu treatment. Content authors can insert valid tokens from their active collection, including custom image/media and repeater data, with populated previews where available.

Verification

• focused editor/token suites: 116 tests passed
• bun run lint
• bun run build
• browser smoke checks for the affected Site and Content interactions