Replace pickadate-rails with native date/time inputs

[mroderick]

Remove the unmaintained pickadate-rails gem and replace its date/time pickers with native HTML5 input type="date" and input type="time".

All virtual attribute parsing (local_date, local_time, expires_at) already goes through DateTimeConcerns#datetime_from_fields, which uses Date.parse and Time.zone.parse — both accept the YYYY-MM-DD and HH:MM formats natively.

I decided to add more tests, i.e. new controller specs, in order to feel confident that tests would notify a contributor that things might break, if they change the inputs' type attributes.

Removed

• pickadate-rails gem and Gemfile.lock entry
• //= require pickadate/* from application.js
• *= require pickadate/* from application.scss
• jQuery init block calling .pickadate() and .pickatime()

Changed

• Workshop, event, meeting forms: native date/time inputs with ISO-formatted values
• Announcement and ban forms: date-only native inputs

New test coverage

• Controller specs with render_views for every form: verify type="date"/type="time" inputs render and pre-fill with ISO format
• Workshop edit: RSVP open/close date and time pre-fill verified
• Announcement edit feature spec: updating expires_at date round-trips correctly

Test results

• Controller specs: 100 examples, 0 failures
• Feature specs: 180 examples, 0 failures

Manual verification steps

Start the app locally (bundle exec rails server), log in via GitHub OAuth as an admin, then:

1. Workshops — /admin/workshops/new

• Create a workshop: verify native date picker for Date, native time pickers for Begins at and Ends at
• Scroll to RSVP Timing: verify native date/time pickers for Open and Close
• Fill all fields, save → "Workshop successfully created"
• Edit the workshop → verify saved values pre-fill correctly in all date/time fields

2. Events — /admin/events/new

• Create an event: verify native date picker for Date, native time pickers for Starts at and Ends at
• Fill all fields, save → "Event successfully created"
• Edit the event → verify saved values pre-fill correctly

3. Meetings — /admin/meetings/new

• Create a meeting: verify native date picker for Local date, native time pickers for Starts at and Ends at
• Fill all fields, save → "Meeting successfully created"
• Edit the meeting → verify saved values pre-fill correctly

4. Announcements — /admin/announcements/new

• Create an announcement: verify native date picker for Expires at (single input, not multiple dropdowns)
• Save → "Announcement successfully created"
• Edit the announcement → change Expires at, save → date persists

5. Bans — /admin/members/:id/bans/new (pick any member)

• Verify native date picker for Date and default value is approximately 1 month from today
• Pick a date, fill reason/note, save → ban created

Regression checks

• No JavaScript errors in browser console (F12 → Console)
• Date/time pickers look like native browser widgets, not styled pickadate widgets
• Required fields still block submission when empty

[mroderick]

I verified this locally. I encourage reviewers to do the same.