feat(v2): add SSH management, ctx integration, themes, detached mode, auto-updater

SSH session management:
- SshSession struct + ssh_sessions SQLite table in session.rs
- CRUD Tauri commands (ssh_session_list/save/delete) in lib.rs
- SshDialog.svelte (create/edit modal), SshSessionList.svelte (sidebar)
- SSH pane routes to TerminalPane with shell=/usr/bin/ssh + args

ctx context database integration:
- ctx.rs: read-only CtxDb (SQLITE_OPEN_READ_ONLY for ~/.claude-context/context.db)
- 5 Tauri commands (ctx_list_projects/get_context/get_shared/get_summaries/search)
- ContextPane.svelte with project selector, tabs, search
- ctx-bridge.ts adapter

Catppuccin theme flavors (Latte/Frappe/Macchiato/Mocha):
- themes.ts: all 4 palette definitions + buildXtermTheme/applyCssVariables
- theme.svelte.ts: reactive store with SQLite persistence
- SettingsDialog flavor dropdown, TerminalPane theme-aware

Detached pane mode (pop-out windows):
- detach.ts: isDetachedMode/getDetachedConfig from URL params
- App.svelte: conditional rendering of single pane without chrome

Other additions:
- Shiki syntax highlighting (highlight.ts, lazy singleton, 13 languages)
- Tauri auto-updater plugin (tauri-plugin-updater + updater.ts)
- AgentPane markdown rendering with Shiki code highlighting
- New deps: shiki, @tauri-apps/plugin-updater, tauri-plugin-updater

v2/src-tauri/tauri.conf.json

@@ -24,6 +24,15 @@
       "csp": null
     }
   },
+  "plugins": {
+    "updater": {
+      "endpoints": [
+        "https://github.com/DexterFromLab/BTerminal/releases/latest/download/latest.json"
+      ],
+      "dialog": true,
+      "pubkey": ""
+    }
+  },
   "bundle": {
     "active": true,
     "targets": ["deb", "appimage"],