fix(security): upgrade @modelcontextprotocol/sdk to 1.26.0 to resolve data-leak advisory

[shwetanaren]

PR description
This PR upgrades @modelcontextprotocol/sdk from 1.25.2 to 1.26.0 to address the high-severity advisory
GHSA-345p-7cg4-v4c7 (cross-client data leak via shared transport/server instance reuse).
Why
pnpm audit reported a High vulnerability affecting the current version.
The issue is resolved in @modelcontextprotocol/sdk >= 1.26.0.
Changes
Bumped SDK version in package.json
Updated pnpm-lock.yaml
Verification
pnpm install
pnpm audit --audit-level high → no High vulnerabilities
pnpm run build → successful
No functional code changes; dependency security update only.

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[shwetanaren]

Hi team
This PR is a dependency-only security update addressing a high-severity advisory in @modelcontextprotocol/sdk.
Please feel free to authorize the deployment if appropriate, or let me know if there’s any additional verification you’d prefer before proceeding.