feat(mvc): redesigned list views with grouping and progress

[kauereinbold]

Summary

• List page redesigned, server-rendered: app header (serif title, date, search pill, New reminder), sidebar nav All/Today/Upcoming/Done with counts and the THIS WEEK progress block, grouped cards (Overdue/Today/Upcoming/Done) with date pills, done toggle, edit and delete actions. View and search are query-string driven (?view=Today&q=text).
• Create/edit/delete are modals over the list page (/Reminders/Create, /Reminders/Edit/{id}, /Reminders/Delete/{id} render the list with the modal open; POST validation errors re-open it with inline field errors). Legacy Bootstrap views, Bootstrap CSS and jQuery removed.
• New RemindersIndexViewModel + ReminderGroups mirror the React reminderGroups util (bucketing, labels, counts, week progress).
• Fixes found during the smoke test: MVC client serialized PascalCase JSON (cpp API 500 on update); edit form posted no id (dotnet API 409); API error keys like LimitDate.Date now map to the form field.
• Selenium suite runs on Linux/WSL: Selenium Manager resolves drivers (bundled .exe removed), headless, null-safe cleanup, base URL default http://localhost:5050 (MVC_BASE_URL override), selectors for the new markup, WaitForAbsence after modal submits (fixed a read-before-navigation race). Firefox row opt-in via MVC_TEST_FIREFOX=1 (snap Firefox hangs under geckodriver on WSL).
• CLAUDE.md: new rule, hand over a test environment plus manual test cases before opening a PR; maintainer can skip.

Remaining from #335: mobile breakpoint under 760px.

Closes #334
Closes #380
Refs #335

Test plan

• dotnet build for Reminders.Mvc and Reminders.Mvc.Test clean
• Runtime smoke test with docker compose --profile api --profile mvc: grouping, counts, progress, view/search filters, toggle, create/edit/delete modals, inline validation errors verified via curl and headless Chrome screenshots
• dotnet test src/test/app/dotnet/Reminders.Mvc.Test against localhost:5050: Chrome row green on 19 of 20 repeated runs (one timeout right after a container rebuild, not reproduced afterwards), Firefox row skipped by default
• Maintainer manual check on the running stack (confirmed in session)
• Known: dotnet API rejects updates on past-date reminders while go/cpp accept (fix(api): align create/update validation and error shape across dotnet, go, cpp APIs #394); the MVC shows the error inline or as an alert.