[MVP] Calendar view for the queue

The queue is a flat list; every mainstream scheduler (Buffer, Later, Publer, Mixpost) has a week/month calendar — it's the signature UI of the category and how managers actually plan.

Scope

• Week and/or month calendar rendering scheduled posts in their time slots
• Each cell shows the post (channel chips, time, truncated text, image/link badges)
• Click a slot → compose scheduled for that time; click a post → open it
• Reuse the existing /postline/queue data (has scheduledAt, providers, hasImage/hasLink)
• Toggle between calendar and the existing list view
• Local-timezone rendering (server stores UTC)

Notes

• Fully buildable + browser-verifiable without live network credentials — good near-term win.
• View: resources/views/queue.stx.