fix: use dynamic anchor id from network prop in AddNetworkButton

[amathxbt]

Bug

AddNetworkButton hardcodes id="mainnet" and href="#mainnet" on the section anchor regardless of which network prop is passed:

<a
  href="#mainnet"    // ❌ always "mainnet"
  id="mainnet"      // ❌ always "mainnet"
  className="subheading-anchor"
  aria-label="Permalink for this section"
></a>

When this component is rendered for both mainnet and sepolia on the same page, two elements share id="mainnet", which:

• Produces invalid HTML (duplicate id attributes)
• Breaks anchor navigation — #mainnet always jumps to the first matching element, making the second network section unreachable via URL hash
• Fails WCAG 2.1 accessibility requirements (each id must be unique per page)

Fix

Derive the id and href dynamically from the network prop:

<a
  href={`#${network}`}   // ✅ e.g. "#ink-mainnet" or "#ink-sepolia"
  id={network}           // ✅ unique per network
  className="subheading-anchor"
  aria-label="Permalink for this section"
></a>

Impact

Anywhere this component is rendered for multiple networks on one page, anchor navigation for all networks except the first is silently broken.