Add native desktop terminal client (crates/desktop)

[pcarrier]

Summary

• New crates/desktop crate (blit-desktop) — a GPU-accelerated native terminal client using winit 0.30 + wgpu 25 + cosmic-text
• Multi-connection architecture: simultaneously connect to Unix sockets, TCP, SSH, and WebRTC shares from a single window
• Persistent remote configuration at ~/.config/blit/remotes.conf (INI-style format)
• BSP tiled layouts with DSL grammar (line(a 2, col(b, c))) and 7 presets
• Dynamic status bar showing terminal count, focused session name, dimensions, and connection status
• Reads ~/.config/blit/blit.conf for font family/size, palette, and custom layouts (same format as web app)
• Mouse support: click, drag, scroll, motion — forwarded to terminal when mouse mode is active, scrollback navigation otherwise
• Cmd/Ctrl+K switcher overlay with search filtering, keyboard navigation, session switching, and new terminal creation

Motivation

Provide a lightweight, GPU-rendered native desktop client for blit that covers the full feature set of the web version. The desktop client avoids browser overhead and enables direct socket/SSH connections without a relay server.

Testing

Manual compilation and launch tested. No automated tests yet — the desktop client is a new standalone binary.

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PR Summary

This PR adds a GPU-accelerated native desktop terminal client (blit-desktop) using winit for windowing, wgpu for rendering, and cosmic-text for text shaping. It connects to blit servers via Unix, TCP, SSH, or WebRTC transports with auto-reconnect, supports BSP tiled layouts, 31 color palettes, mouse tracking, scrollback, and a keyboard-driven session switcher overlay.

• New crates/desktop crate with full GPU rendering pipeline (rect + glyph shaders, dynamic glyph atlas)
• Connection management with async tokio tasks, EventLoopProxy-based wakeup, and reconnection via ReconnectNeeded events
• Transport abstraction supporting Unix sockets, TCP, SSH (via ControlMaster), and WebRTC share connections
• Terminal state rendering converting blit_remote::TerminalState cells to GPU vertices with cursor rendering
• BSP layout system with DSL parser and 7 tiled layout presets
• Overlay system with functional Cmd+K session switcher (search, arrow navigation, actions) and help screen
• Mouse event handling (click, drag, scroll, motion) forwarding to server based on terminal mouse mode
• User configuration via ~/.config/blit/remotes.conf and ~/.config/blit/blit.conf (font, palette, layout settings)
• Status bar with session info, title, dimensions, and connection indicator

Issues

All clear! No issues remaining. 🎉

9 issues already resolved

• If the server sends a cell with content_len > 4 (the 3-bit field allows 0-7), GlyphKey.bytes is only [u8; 4] and copy_from_slice will panic. Valid UTF-8 caps at 4 bytes so this isn't triggered today, but there's no guard against malformed data. (fixed by commit 5a05d15)
• Terminal freezes after initial render: process_server_events() only runs inside RedrawRequested, but with ControlFlow::Wait and no wakeup mechanism for the mpsc channel, no redraws are requested after the first frame. Server output queues up but is never displayed until the user interacts with the window. (fixed by commit e217f87)
• Every FrameUpdate sends Command::Resize { pty_id, rows: 0, cols: 0 } to the server, which is a resize to zero dimensions. This fires on every frame, flooding the server with invalid resize commands. (fixed by commit 5a05d15)
• No tokio runtime is initialized — tokio::spawn() in ConnectionManager::connect() will panic with "must be called from the context of a Tokio runtime" as soon as connect_remotes() fires during resumed(). The default local remote has autoconnect = true, so this crashes on every startup. (fixed by commit 5a05d15)
• assign_sessions in bsp.rs uses format!("{:p}", *c as *const K) for deduplication, which compares pointer addresses instead of values. The same session appearing in both lru and live will have different addresses and can be assigned to multiple panes. (fixed by commit 5a05d15)
• Status bar panics on multi-byte UTF-8 titles: &name[..max_chars - 1] byte-slices a &str using a character count as byte index. If the slice point falls within a multi-byte character (CJK, emoji), the client panics. (fixed by commit e217f87)
• RedrawRequested unconditionally calls w.request_redraw(), creating an infinite redraw loop despite ControlFlow::Wait. This burns 100% CPU/GPU continuously. Should only request redraw when needs_redraw is true or the blink timer fires. (fixed by commit 5a05d15)
• Reconnection is broken: after disconnect, connection_task creates a new mpsc channel but immediately drops the sender (new_tx), so cmd_rx.recv() in the writer task returns None instantly. The manager's ConnectionHandle.cmd_tx still references the old dead sender, so no commands can reach reconnected sessions. (fixed by commit 5a05d15)
• Overlays remain non-functional after the fix commit: overlay text glyphs are still never rendered (empty &[] passed to renderer), and keyboard input is still silently consumed without being dispatched to overlay handlers. Overlays can only be opened (showing an empty panel) and closed. (fixed by commit 5ac12e1)

CI Checks

All CI checks passed on commit 5ac12e1.