feat(sidebar): add window navigation and user tmux config import

[redlotusaustin]

Summary

Two enhancements to the session management sidebar:

1. Window navigation — Tmux windows appear as expandable sub-items under sessions in the sidebar. Press Right arrow or Enter to expand, Left arrow to collapse. Window indent indicators (▶/▼) show expand/collapse state. Active windows show a ● dot. The expandSidebar config auto-expands all sessions on load.

2. Import user tmux config — A config toggle (c → "Import user tmux config") that sources the user's ~/.tmux.conf into Agent View's isolated tmux server. The user's config is sourced last so it takes full precedence over Agent View's default status bar, colors, and settings.

Both features are off by default — no behavior change for existing users.

Changes

• src/core/types.ts — Added TmuxWindow interface
• src/core/tmux.ts — Added listWindows(), selectWindowSync(), setUserTmuxImport()
• src/core/tmux.conf — Added conditional source-file ~/.tmux.conf at end
• src/core/config.ts — Added importUserTmuxConfig and expandSidebar config fields
• src/tui/util/groups.ts — Extended GroupedItem with window type
• src/tui/routes/home.tsx — Window expansion, navigation, indicators, collapse behavior
• src/tui/component/dialog-settings.tsx — Settings entries for both new toggles

Keybinds

Key	On session	On window	On group
Right/Enter	Expand windows → attach	Select + attach	Expand
Left	Collapse windows → collapse group	Collapse windows	Collapse
Up/Down	Navigate items	Navigate items	Navigate items

Notes

• listWindows() uses execFileAsync to avoid shell escaping issues with tmux format strings
• Window items use a plain renderFlatItem() function instead of nested <Show> to avoid OpenTUI invisible text rendering bugs
• expandSidebar auto-expand respects manual collapses via a collapsedSessions signal
• User tmux config is sourced last; a note warns about reserved Ctrl+Q/K/L/T/O/]/\ keybinds