Flag value panel is hard to read and edit

### Description
The panel used to view and edit a flag value opens in a fixed width side panel that cannot be resized, and there is no option to edit a flag value on a full page. Reading a longer value at a glance is difficult. For JSON the editor already provides syntax highlighting and live validation, but there is no pretty printing or structured editor, so a user has to keep commas and braces intact by hand.

### Requested improvements
- A resizable panel, or an option to edit a flag on a full page for more screen space
- Pretty printing or a structured editor for values, on top of the existing highlighting and validation

### Impact
Developers flagged value readability as a recurring pain point. Manually maintaining JSON structure also raises the risk of an accidental bad edit.

The issue names no files, tests, or entry points; start by locating the flag value panel and its existing JSON highlighting and validation. Done means providing more screen space through resizing or a full-page editor, plus pretty printing or structured editing while preserving validation.

Written by the indexing model from the issue text.