feat: multi-field forward form with Tab cycling

Replace single-line prompt with form-based forward input:
- Separate Type/Host/Port fields
- Tab/Shift+Tab cycles focus, Tab on Type field cycles mode values
- Address auto-split into host+port for edit
- COM port excludes port field
- Form render with focused field indicator

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/tui/model.go

@@ -61,6 +61,13 @@ type Model struct {
 	promptInput  textinput.Model
 	promptSubmit func(string)
 
+	formActive  bool
+	formTitle   string
+	formFields  []textinput.Model
+	formLabels  []string
+	formFocus   int
+	formSubmit  func([]string)
+
 	completionActive     bool
 	completionBase       string
 	completionCandidates []string
@@ -262,6 +269,10 @@ func (m *Model) View() string {
 		return fillScreen(m.width, m.height, base)
 	}
 
+	if m.formActive {
+		return renderCenteredModalContent(m.width, m.height, m.renderForm())
+	}
+
 	if m.promptActive {
 		return renderCenteredModalContent(m.width, m.height, m.renderPrompt())
 	}