[docs] Generate human-readable error code pages

[KayleeWilliams]

Why

The error registry in packages/internals/error-codes exists with machine-readable codes and the TSDoc CI check is great - but each error only has a link to a docs page that does not exist yet. When a customer hits an error, they need "what happened, why, how to fix" - this compounds: it drops support load and makes the SDK feel cared-for.

Scope

• Auto-generate one MDX page per error code from the registry
• Each page: symptom, root cause, common triggers, remediation, code example, related codes
• Index page listing all codes by category
• CI check: every code in the registry has a docs page, every docs page has a live code
• Link to hosted docs from the error docsLink field

Priority: P1 - beta blocker

[devcool20]

Hey @KayleeWilliams, is this issue partially fixed??
because the current repo already has per-code MDX pages(76).
also, the issue says docsLink, but the code uses docsUrl.