feat(events): move bulk-select checkboxes inside programme event cards

[mindsers]

Summary

• Move the bulk-select checkbox from outside each programme event card into a reserved slot inside, so cards keep uniform widths regardless of the current user's edit rights.
• Add a selected-state card treatment (subtle tint + ring) and a stronger hover; fade the resting checkbox and reveal it on hover / check / focus.
• Align the sticky bulk bar, per-week checkbox, and per-card checkbox on the same x-axis (pl-5 sm:pl-7 matches the card's 4px border + sm:px-6 padding).
• Always reserve the 4px kind-color slot on the card border — cards without a kind color use transparent and stay in the same column.
• Collapse the checkbox column entirely on weeks with zero editable events; add aria-labels to all three checkbox tiers; upgrade the sticky bar to a semantic <section>.

Test plan

• As a Programme Manager, every card shows a faded checkbox that fills in on hover
• Selecting a card shows the tint + ring; sticky bulk bar drops in with count and actions
• Hovering a selected card keeps the primary tint instead of the muted hover
• All three checkbox tiers (sticky bar / week / card) sit on the same vertical axis at both mobile (px-4) and desktop (sm:px-6) card padding
• Cards without a kind color align with colored cards
• Weeks where the user has no editable events collapse the checkbox column
• Screen reader announces per-event, per-week, and bulk-action labels