New dark theme to schedule

[nikoshell]

• Dark background with dot-grid + gradient pattern on schedule pages
• Update schedule grid to use CSS grid with proper placement for
  ep-session cards, time column, breaks, and posters
• Restore old Inter Tight typography for body, headlines, and navbar
• Add visible borders to time column and room-change elements
• Room-change and day-end use solid background
• Headlines are anchor-linked (clickable heading links)
• Breaks center-aligned at top with 20px padding
• Fix poster session overlap (ep-session.poster grid rules)
• Fix session grid placement (add :global(.ep-session) rule)

[europython-society]

Preview available

Key	Value
url	https://ep2026-schedule.ep-preview.click
last update	2026-05-27T21:43:41.025Z

[nikoshell]

Direct link https://ep2026-schedule.ep-preview.click/schedule

[clytaemnestra]

Thanks for the PR! Overall looks good, I have only two notes:

• Let's make the font a bit bigger, it's a bit hard to read
• I'm not sure what do different backgrounds (dots, stripes etc.) in tiles mean, let's maybe have all of them the same or if there's some logic in it (for example data&MR = dots, core Python = stripes etc.), let's add legend