Adds title frontmatter to 84 docs pages that were missing it. The vocs.config.ts uses titleTemplate: '%s ⋅ Tempo', so each title renders as {title} ⋅ Tempo in the browser tab and OG tags.

What changed:

• 80 files had existing frontmatter with description but no title — added title
• 4 files had no frontmatter at all — added full --- block with both title and description

Sections covered: guide/issuance, guide/node, guide/payments, guide/stablecoin-dex, guide/tempo-transaction, guide/use-accounts, index, learn, protocol, quickstart, sdk