fix: override axios to >=1.15.2 to resolve multiple CVEs

[MathurAditya724]

Adds axios to pnpm.overrides (same pattern as the existing protobufjs override) to force resolution to >=1.15.2, which resolves 15 open Dependabot alerts covering prototype pollution, SSRF, header injection, CRLF injection, and DoS vulnerabilities.

Axios is a transitive dependency (pulled in via @atproto packages and vitepress), so an override is the correct fix.

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Coverage Report for ./packages/client/

Status	Category	Percentage	Covered / Total
🔵	Lines	13.64%	52 / 381
🔵	Statements	13.13%	52 / 396
🔵	Functions	9.6%	17 / 177
🔵	Branches	14.45%	12 / 83

File Coverage

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Generated in workflow #295 for commit acf18d6 by the Vitest Coverage Report Action

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commit: acf18d6

[MathurAditya724]

all CI checks passed (build, ci, semantic PR, netlify deploy, continuous releases). self-review clean — the change is just a pnpm.overrides entry bumping axios to >=1.15.2, plus the lockfile regen. marked ready for review.