fix(ui): keep the saved sidebar width when a narrower sidebar clamps it

The workspace context panels and Favorites share one stored
`sidebar-width` but clamp it to different limits. Loading wrote the
clamped value back, so visiting Settings (max 400) cut a categories
panel widened to 520 down to 400; the saved width could only shrink.

Load now clamps for rendering only. Legacy alias keys migrate their raw
value, an unparseable value falls back to the default without a write,
and only a drag that changes the width persists — a click on the handle
no longer saves the clamped width either.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/iptvnator-ui-guidelines.md

@@ -212,6 +212,14 @@ directive-generated `.resize-handle` sets this centrally in `resizable.scss`.
 The shared live-layout sidebar reserves 8 px at its right edge so the inward
 half of the 12 px resize handle cannot cover the channel scrollbar.
 
+## Resizable Sidebar Widths
+
+Workspace context panels and Favorites share one `sidebar-width` key (its
+legacy aliases map onto it) but have different limits. `ResizableDirective`
+renders the stored width clamped to the host's own limits and never writes
+that clamped value back: only a drag that changes the width persists, so a
+narrow sidebar such as Settings cannot shrink the width a wider one saved.
+
 ## Keyboard Scrolling and Channel Focus
 
 `ChannelScrollFocusDirective` belongs on the actual channel scroll owner,