## Why
UI tree limits previously applied during rendering, silently dropping content
beyond the budgets. Validate the whole JSON tree before rendering so oversized
inputs are rejected, including content outside the visible line.
## What changed
- Add a `UiTree` string parser that limits JSON to 64 KiB, nesting depth to 16,
non-null nodes to 256, and total string content to 16 KiB of UTF-8.
- Represent text as string leaves or `text` elements with children. Remove node
keys, `spacer`, and `divider` elements.
- Require an explicit `row` gap as a non-negative JavaScript-safe integer measured
in terminal columns. Bound rendered spacing by the viewport and skip empty
children when inserting gaps.
- Update footer content and built-in status lines to use the revised tree format.
## Testing
Add coverage for malformed elements and gaps, whole-tree size boundaries, URL
length limits, large-gap rendering, and bounded UTF-8 prefixes for directly
constructed text. Update hyperlink and footer clipping tests for the new format.
GitOrigin-RevId: 3c00881d3e7f2d79d11aa188f64f0725cd47ee68
## What changed
- Add the disabled-by-default `tui_extensions_statusline` feature to render configured status items and their picker preview through a shared UI tree renderer.
- Support text, HTTP(S) links, rows, spacers, dividers, and gaps with rendering budgets, text sanitization, and width-aware truncation that keeps the ellipsis outside hyperlinks.
- Use plain text for the extension status line and hide the picker's theme color toggle while preserving the saved color preference.
## Testing
Add coverage for tree serialization and URL validation, Unicode widths, hyperlink clipping, picker previews, color preference preservation, and token usage updates across renderer switches.
GitOrigin-RevId: a6b87c2b1096765d61296d73e142834fcd53ceee
Joe Savona