Move notes below video titles in desktop table

[arena-ai-coding-agent]

Summary

• show only the filtered and total video counts in the inventory heading
• switch from the desktop table to mobile-first cards below 1440px, before columns become clipped
• split datetimes into date and time lines only in the compact desktop table
• keep mobile-card datetimes on one non-wrapping line and preserve one-line dates on wide desktops
• use the same compact 1rem outer gutter at every screen width
• keep only the add/edit control in each desktop Note cell
• use the same add-note pen icon for note controls on desktop and mobile
• replace the pen with a green save check and red cancel control while editing
• support Enter to save and Escape to cancel without saving
• make editable note text slightly brighter than viewed note text
• show existing note text directly below its video title using the existing small text style
• open the multiline note editor below the video title when the Note icon is clicked
• make view and edit modes share the same text position, typography, and spacing
• remove the editor border, background, padding, and resize handle, and auto-size it to its content
• scale displayed notes and note editors proportionally with video titles on desktop and mobile
• narrow the Note column so the title and note content have more room
• inline the filter utilities in index.html and remove the standalone filters.js file

Tests

• node --test tests/filters.test.js