chore: update ajv to 8.20.0 and pin fast-uri to fix high severity CVEs

[danielmrdjanov]

Summary

• Bumps ajv from 8.18.0 → 8.20.0
• Adds pnpm.overrides to pin fast-uri >= 3.1.2, resolving two high-severity
  vulnerabilities in the transitive dependency

Security advisories fixed

CVE	Package	Vulnerable	Patched	Description
GHSA-q3j6-ggpj-74h6	fast-uri	<= 3.1.0	>= 3.1.1	Path traversal via percent-encoded dot segments
GHSA-v39h-62p7-jpjc	fast-uri	<= 3.1.1	>= 3.1.2	Host confusion via percent-encoded authority delimiters

Why the override?

ajv@8.20.0 still declares fast-uri: ^3.0.1, which includes the vulnerable
range. The pnpm.overrides entry forces resolution to >= 3.1.2 across the
entire dependency tree and can be removed once ajv tightens its own range.

Validation

• pnpm audit → no known vulnerabilities found
• All 344 tests pass