style: Extract UI constants and refactor main view rendering (#30)

- [x] Add golangci-lint configuration with gocritic ifElseChain disabled
- [x] Rename error variables to avoid shadowing (createErr, watcherErr, watchErr, etc.)
- [x] Replace `interface{}` with `any` type alias throughout codebase
- [x] Add package-level documentation comments to all internal packages
- [x] Reorder struct fields alphabetically for consistency
- [x] Extract UI constants (terminal dimensions, column widths, colors) to constants.go
- [x] Refactor BubbleTeaUI main view rendering into smaller helper functions
- [x] Simplify nested conditionals and improve code clarity
- [x] Add `isForwardDisabled()` helper method to BubbleTeaUI
- [x] Update file permissions from 0644 to 0600 in config tests
- [x] Add `#nosec` comments and error suppression where appropriate
- [x] Improve test table struct field ordering for readability
- [x] Fix resource parsing in AddForward using strings.SplitN
- [x] Add comprehensive tests for new UI helper functions and constants

internal/forward/portcheck.go

@@ -99,9 +99,9 @@ func getProcessNameByPIDWindows(pid string) string {
 
 // PortConflict represents a local port that is already in use.
 type PortConflict struct {
-	Port     int    // The conflicting port number
-	Resource string // The forward resource that needs this port
-	UsedBy   string // Process information (PID, command) using the port
+	Resource string
+	UsedBy   string
+	Port     int
 }
 
 // PortChecker checks port availability on the local system.
@@ -146,7 +146,7 @@ func (pc *PortChecker) isPortAvailable(port int) bool {
 	if err != nil {
 		return false
 	}
-	_ = listener.Close()
+	_ = listener.Close() // Best-effort cleanup; port check succeeded, Close error is non-critical
 	return true
 }