Reset global editor keybindings to defaults in beforeEach for
session-selector-rename and tree-selector tests. Pass
KeybindingsManager.inMemory() to SessionSelectorComponent in tests
to avoid reading user keybindings.json.
Closes#2360
* Add session renaming in interactive mode resume picker
Session list now displays last message timestamp as modified time
instead of file mtime. Ctrl+N enters rename mode in the interactive
resume picker, allowing quick session renaming without leaving the
selector. Rename hint is shown only in interactive mode, not in the
CLI --resume picker./
* Add docs entry for renaming in picker
* Update shortcut to ctrl+r for session renaming
