fix(ui): rendering issues when opening files with -t flag

When passing a file via the CLI with the TUI flag (-t), the -w flag was
ignored and window resizing would result in a blank screen. This was
caused by the file content not being stored in currentDocument.Body
during Init(). Consequently, the first WindowSizeMsg triggered a
re-render with an empty body, discarding the initial content.

Replaced manual file reading in Init() with loadLocalMarkdown() to
ensure the body is correctly stored and a fetchedMarkdownMsg is
emitted. This ensures content is preserved during re-renders and that
the word wrap width is correctly applied.

Fixes #878

ui/ui.go

@@ -190,13 +190,7 @@ func (m model) Init() tea.Cmd {
 	case stateShowStash:
 		cmds = append(cmds, findLocalFiles(*m.common))
 	case stateShowDocument:
-		content, err := os.ReadFile(m.common.cfg.Path)
-		if err != nil {
-			log.Error("unable to read file", "file", m.common.cfg.Path, "error", err)
-			return func() tea.Msg { return errMsg{err} }
-		}
-		body := string(utils.RemoveFrontmatter(content))
-		cmds = append(cmds, renderWithGlamour(m.pager, body))
+		cmds = append(cmds, loadLocalMarkdown(&m.pager.currentDocument))
 	}
 
 	return tea.Batch(cmds...)