Allow template authors to highlight customizable areas

**Job Story**

When _authoring a schema template made up of multiple sub-schemas_, I want _to mark and label which sections or fields are customizable, along with a short note explaining what can be changed_, so I can _make it easy for anyone using the template to immediately see what's editable without opening each schema one by one to check if it's locked._

**Acceptance Criteria**

* Template authors can flag specific sections or fields within a template as "customizable"
* Each flagged customizable area supports a short note/description explaining what can be changed and how
* Customizable flags and notes are visible in the template editor
* Customizable flags and notes are also visible in the Manage Schemas tab, without needing to open each sub-schema individually
* Non-flagged sections/fields are clearly distinguishable as locked/non-customizable (visual contrast between the two states)
* Flags and notes persist and remain accurate as templates are edited or sub-schemas are reordered

**Artifacts & Considerations**

* Consider a consistent visual pattern (badge, icon, highlight color) to represent "customizable" across both the template editor and Manage Schemas tab