Sponsor tiers: Add discounted tickets to Silver & Gold, TV to Platinum

[hypha]

@artcz has requested the following updates to sponsor tiers:

• Add discounted tickets to Silver and Gold
• Include TV & stand in the Platinum booth setup

Places to update:

1. Website: sponsor-tiers.astro
2. Full sponsorship opportunities PDF
3. Sponsor mockup PDF
4. Sponsor lookup table
5. Coordinate with booth builder (re: TV setup for Platinum)

Only item 1 is in scope for this website repo. The rest are noted here for future reference, as an issue here is linked to the 2025 project and may be useful context for others.