feat: add toolbar_badge() and update_toolbar_badge() (#1316)

[elnelson575]

Summary

• Adds toolbar_badge() — a pure display element for showing status text and icons inside a toolbar(), using Bootstrap's badge component (text-bg-{color}, optional rounded-pill, optional border for outline-only style)
• Adds update_toolbar_badge() — server-side update function using sendCustomMessage (not an input binding) to update label, icon, color, border, pill, and show_label
• Adds toolbarBadge.ts JS handler and .bslib-toolbar-badge SCSS rule; updates the toolbar example app with live badge demos

Design decisions

• Pure display element (no Shiny input binding) — badge state flows one way from server to browser; no input$badge_id side effects or bookmarking noise
• Follows toolbar_input_button() aria pattern — randomly generated label_id, hidden attribute + aria-labelledby so screen readers read the label even in icon-only mode
• Tooltip defaults to !show_label — icon-only badges get a tooltip by default, matching the button family
• border = TRUE for outline style — uses Bootstrap's border border-{color} text-{color} utilities instead of text-bg-{color}; data-bslib-color and data-bslib-border attributes track state so update_toolbar_badge() can toggle either independently

Sample images

Toolbar badge showing record numbers

Toolbar badge showing "Live"

Toolbar badge in text input showing number of messages

Test plan

• 186 toolbar tests pass (devtools::test(filter = "toolbar"))
• toolbar_badge("Active") renders with text-bg-secondary badge classes
• toolbar_badge("Active", border = TRUE) renders with border border-secondary text-secondary classes (no text-bg-*)
• Icon-only badge wraps in bslib-tooltip with {id}_tooltip id
• update_toolbar_badge() sends bslib.update-toolbar-badge custom message with only provided fields
• Run shiny::runExample("toolbar", package = "bslib") and verify: record count badge (outline pill) shows in footer, activity status badge cycles with icon+color on refresh, chat message count updates reactively

Closes #1316