Add live-linked sequencer templates

[isbeorn]

Purpose

Adds Linked Templates for the Advanced Sequencer. A linked template keeps a live reference to the source template instead of copying it, shows the materialized template content as a read-only preview, supports edit/save back to the user template, refreshes automatically when templates change, and stores per-use target overrides for DSO templates.

How Was It Tested?

• Ran targeted sequencer tests for linked templates, template saving, drag/drop hit testing, and move-up/down placement behavior.
• Manual UI testing.

AI / Tooling Disclosure

OpenAI Codex was used to help implement, review, and document this change.

✅ PR Checklist

• All unit tests pass
• UI changes tested across Light, Dark, and Night themes
• Plugin API compatibility reviewed
  • No breaking changes to interfaces
  • No changes to plugin-facing method/class signatures
• RELEASE_NOTES.md updated
• Documentation updated

Related Issues

N/A

Screenshots

Template Sidebar

Linked Template In Sequence

Edit Template Mode

Target overrides

Enhanced context menu

Additional Notes

Linked templates are intentionally created explicitly via Ctrl-drop or the linked-template menu. Normal
template drops still create independent copies.