Add bulk asset management (enable/disable + edit multiple assets at once) #3046

Summary

There is no way to act on multiple assets at once in the web UI. Each asset must be enabled/disabled or edited individually, which is painful for operators with many assets. This has been requested repeatedly on the forum over several years.

Requested capabilities

• Enable/disable all assets (or a selected subset) in one action.
• Edit common fields (start/end date, time-of-day, duration) across multiple selected assets at once.

Current state

• The asset table has a per-row enable checkbox only (src/anthias_server/app/templates/_asset_row.html). There is no multi-select, no "select all", and no bulk-action bar.
• The REST API is per-asset by design (see the comment at src/anthias_server/api/views/v2.py:1133), so the only current workaround is scripting one call per asset.

Suggested approach

• Add row selection (checkboxes + select-all) and a small bulk-action bar: Enable, Disable, Edit (dates/time/duration), Delete.
• Back it with either a loop of the existing per-asset calls or a new batch endpoint.

Forum threads (recurring over the years)

• https://forums.screenly.io/t/200 Enabling & disabling assets in bulk
• https://forums.screenly.io/t/221 Turn all assets on/off at once
• https://forums.screenly.io/t/432 Activate/Deactivate all assets button
• https://forums.screenly.io/t/606 Activate all assets (+ random)
• https://forums.screenly.io/t/1525 Edit assets in bulk (dates/times)