Add column mapping onboarding: info icons and first-visit tour

[emares17]

Summary

• Info icons added next to Barcode Column, Text Fields, and Header Row labels — clicking opens a popover with a plain-language explanation and a worked example
• First-visit tour — a floating card that walks new users through the column mapping section in 4 steps; localStorage-gated so it only appears once, on /dashboard or /upload
• Shared content constants — popovers and tour pull from the same file so copy stays in sync
• Cleared misleading defaults — replaced pre-filled text field rows (column 1 "Location", column 4 "Unit") with a single blank row to prevent silent misconfiguration
• PostHog tracking — column_mapping_tour_shown, column_mapping_tour_dismissed, column_mapping_help_opened events added

Test plan

• Log in — tour card should appear on /dashboard bottom-right
• Step through all 4 tour steps, confirm "Got it" on the last step dismisses it
• Reload — tour should not reappear
• Open incognito — tour should reappear
• Click the info icon next to each of the three column mapping fields — popover opens with correct content
• Verify column mapping section starts with one blank text field row (no pre-filled Location/Unit values)
• Check PostHog for the three new events

Generated with Claude Code

[railway-app]

🚅 Deployed to the BarcodeGenerator-pr-17 environment in LabelGenius

Service	Status	Web	Updated (UTC)
LabelGenius-Frontend	✅ Success (View Logs)	Web	Apr 28, 2026 at 11:12 pm
LabelGenius-Backend	✅ Success (View Logs)	Web	Apr 28, 2026 at 11:11 pm