Update disk performance docs: upgrades are now self-serve, add tier table + screenshots

Problem

The Pricing model page still says disk performance upgrades are Enterprise-only and require contacting sales. That is no longer true — disk performance is now a self-serve add-on that any project can upgrade directly from the Cloud dashboard.

Current text (capabilities/platform/billing/pricing_model.mdx, L19–21):

High Performance Disk (Enterprise)

Enterprise accounts can enable High Performance Disk on L tiers and above. It provides roughly 5x the IOPS and disk bandwidth of standard disk, which improves indexing throughput and search speed for disk-bound workloads. Contact sales@meilisearch.com to enable it.

Two things are wrong or missing:

1. It routes users to sales for something they can now buy themselves in the dashboard.
2. It gives no tier table — no IOPS, throughput, or prices — so users can't tell what they'd be buying.

Proposed update

Replace the section with the following (rename High Performance Disk (Enterprise) → Disk performance):

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Disk performance

Every resource-based project includes Standard disk performance. If disk I/O is capping your indexing or search speed, you can upgrade your project's IOPS and throughput directly from your dashboard — no need to contact sales.

Tier	IOPS	Throughput	Price
Standard	3,000	125 MB/s	Included
High	5,000	200 MB/s	$52/month
Extra	10,000	300 MB/s	$168/month
Max	15,000	1,000 MB/s	$380/month

To upgrade, go to your project's Infrastructure tab and select Upgrade disk performance, then choose a tier.

The IOPS Usage and Disk Throughput charts on the same tab show your current consumption against your tier limit. If you are regularly hitting the dashed tier-limit line, you are disk-bound and a higher tier will help.

You can also manage the add-on from Project Settings → Disk Performance, which shows your current configuration.

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Screenshot notes

• The three images above are cropped and ready to commit. Suggested path, matching the existing convention: assets/images/platform/billing/.
• The modal shot is cropped to the dialog itself — the raw capture had it overlaid on a dimmed Infrastructure tab, which reads badly in docs.
• Source of truth for the numbers is the in-app changelog announcement, included below for reference only. Not for the docs — the table is cut off mid-scroll, so the Max row isn't visible.

Changelog announcement (reference)

Questions for @qdequele

• Prices and tiers: the numbers above are transcribed from the dashboard on my project. Do they vary by region or resource tier, the way compute/disk pricing does? If so the table needs a "prices may vary by region" caveat like the one above it.
• Availability: does the old "L tiers and above" restriction still apply, or is the add-on available on every resource-based tier now? The modal didn't show any gating.
• Usage-based projects: is this add-on resource-based only, or does it apply to Build/Custom too?
• Is there anything left that still genuinely requires contacting sales here (e.g. above Max)?

Happy to open the PR once these are confirmed.

Scope

• Rewrite the section in capabilities/platform/billing/pricing_model.mdx
• Add the tier table
• Commit the three screenshots to assets/images/platform/billing/
• Grep for other pages that point users to sales for disk performance