feat(coding-agent): add resume as configurable keybinding action Allow users to bind a key to open the session resume selector, matching the pattern of newSession, tree, and fork actions.
Allows extension commands to programmatically switch to a different session file via ctx.switchSession(sessionPath). fixes #1187
Add newSession, tree, and fork as configurable keybinding actions. All unbound by default. Users can configure in keybindings.json. Closes #1088