Pr 1724 (#1939)

* feat(coding-agent): add fold/unfold to tree branch navigation

Remap left/right arrow keys in the session tree to jump between branch
segment starts (first child of each branching point). Left on a foldable
node (root or segment start) folds it, hiding its descendants. Right on
a folded node unfolds it. Nested fold state is preserved. Search and
filter changes reset all folds.

Folded branches show ⊞ in the connector (├⊞/└⊞) or as a prefix for
roots. Active path marker • appears after the fold indicator.

Add Page Up/Down support for paging through the tree list, consistent
with session selector and config selector.

* feat(coding-agent): improve tree branch folding closes #1724

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Co-authored-by: Sviatoslav Abakumov <dust.harvesting@gmail.com>

packages/coding-agent/README.md

@@ -211,7 +211,7 @@ pi --session <path>    # Use specific session file or ID
 
 <p align="center"><img src="docs/images/tree-view.png" alt="Tree View" width="600"></p>
 
-- Search by typing, page with ←/→
+- Search by typing, fold/unfold and jump between branches with Ctrl+←/Ctrl+→ or Alt+←/Alt+→, page with ←/→
 - Filter modes (Ctrl+O): default → no-tools → user-only → labeled-only → all
 - Press `l` to label entries as bookmarks