docs: rewrite TUI Layer — tab system, orange theme, multi-session SSH

docs/plans/2024-06-22-hostkeeper-design.md

@@ -144,22 +144,47 @@ hostkeeper completion                    # Shell completion setup
 
 ### 2. TUI Layer (Interactive Interface)
 
-**Framework:** Bubble Tea (recommended for modern, maintainable TUI)
+**Framework:** Bubble Tea (event-driven TUI) + Lipgloss (styling)
 
-**Main Screens:**
+**Theme:** Orange/light color palette (`#FF6B00`, `#FF9F43`, `#FFB800`) — visually distinct from native terminal to signal the user is inside Hostkeeper
-- **Host List:** Grid/List view with status indicators
-- **Connection Manager:** Active connections, quick actions
-- **SFTP Browser:** Dual-pane file browser (Phase 2)
-- **Key Manager:** SSH keys list, import/export, generate
-- **Snippet Manager:** Command snippets with variables
-- **Settings:** Config management, preferences
 
-**TUI Features:**
+#### Tab System Architecture
-- Event-driven architecture
+
-- Responsive layout
+```
-- Keyboard navigation
+┌─ Hosts ──── Server Nico ── SFTP ── Keys ── Settings ────────┐
-- Mouse support (optional)
+│                                                               │
-- Quick actions (`/` search, `n` new, `Ctrl+S` SFTP, etc.)
+│  [content of active tab]                                      │
+│                                                               │
+├───────────────────────────────────────────────────────────────┤
+│ Ctrl+Q:close  Ctrl+Tab:next  Shift+Tab:prev  ↑↓:nav  /:search│
+└───────────────────────────────────────────────────────────────┘
+```
+
+**Tab Types:**
+- **HostsTab** — Host list with search, filter, sort, keyboard navigation
+- **SessionTab** — Live interactive SSH session (input/output piped via Go SSH client)
+- **SFTPTab** — Remote file browser with upload/download operations
+- **KeysTab** — SSH key management (list, generate, import)
+- **SnippetsTab** — Command snippets with variable substitution
+- **SettingsTab** — Application configuration
+
+**SessionTab Internals:**
+- Connect via Go SSH client with stored credentials (password auto-injected)
+- 2 goroutines per session: stdin → SSH channel, SSH stdout → TUI render
+- Terminal resize event → `WindowChange` via SSH channel
+- `Ctrl+Q` disconnects session and closes tab
+- Multiple session tabs can be open simultaneously (e.g. connect to 3 servers at once)
+
+**Keyboard Navigation:**
+| Key | Action |
+|-----|--------|
+| `Ctrl+Tab` / `Shift+Tab` | Cycle tabs forward/backward |
+| `Ctrl+N` | New tab (add host / new connection) |
+| `Ctrl+Q` | Close current tab / disconnect session |
+| `↑` / `↓` | Navigate lists (hosts, keys, files) |
+| `Enter` | Select host / open directory / confirm |
+| `/` | Search/filter within active tab |
+| `q` | Quit Hostkeeper (confirmation dialog) |
 
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