chore: add VHS tooling for uptop TUI screenshots

Backfill tool, crop tool, demo tape, seed data, and setup script
extracted from the uptop repo for clean separation.

demo.tape

@@ -0,0 +1,72 @@
+Set Shell "bash"
+Set Width 1400
+Set Height 800
+Set FontSize 14
+Set Padding 20
+Set Framerate 15
+Set TypingSpeed 50ms
+
+# Seed demo data + start uptop (UPTOP_DEMO=1 → stable pulse dot for stills).
+Hide
+Type "bash vhs/setup.sh /tmp/uptop-vhs.db"
+Enter
+# Warm-up: push heartbeat lands (~10s) and initial checks settle. Kept short so every
+# capture stays inside the 60s node-freshness window (consistent "3 probes" footer).
+Sleep 18s
+Show
+Sleep 2s
+
+# 1. Sites — hero shot: mixed states, history sparklines, SSL, retries.
+Screenshot vhs/screenshots/monitors.png
+Sleep 1s
+
+# 2. Detail — drill into Nextcloud (6th row from the top).
+Down
+Sleep 150ms
+Down
+Sleep 150ms
+Down
+Sleep 150ms
+Down
+Sleep 150ms
+Down
+Sleep 300ms
+Type "i"
+Sleep 2s
+Screenshot vhs/screenshots/detail.png
+Sleep 500ms
+Escape
+Sleep 1s
+
+# 3. Alerts — channels with health dots + recent "last sent".
+Tab
+Sleep 1500ms
+Screenshot vhs/screenshots/alerts.png
+Sleep 500ms
+
+# 4. Logs — chronological, severity-coloured event stream.
+Tab
+Sleep 1500ms
+Screenshot vhs/screenshots/logs.png
+Sleep 500ms
+
+# 5. Nodes — distributed probes across regions.
+Tab
+Sleep 1500ms
+Screenshot vhs/screenshots/nodes.png
+Sleep 500ms
+
+# 6. Theme — cycle to the next theme, return to Sites for an alternate-palette hero.
+Type "T"
+Sleep 500ms
+Tab
+Sleep 200ms
+Tab
+Sleep 200ms
+Tab
+Sleep 1s
+Screenshot vhs/screenshots/theme.png
+Sleep 500ms
+
+Type "q"
+Sleep 1s