Resolve npm security alerts

[samlown]

Summary

• refresh the root WASM and worker npm lockfiles to patched transitive dependency versions
• update browser-sync and markdownlint-cli
• require a patched immutable version
• resolve all currently open Dependabot advisories reported for both npm trees

This PR is based on #35 so it contains only the npm security remediation. Once #35 merges, GitHub can retarget this PR to main.

Testing

• go test ./...
• npm audit --prefix wasm — 0 vulnerabilities
• npm audit --prefix wasm/worker — 0 vulnerabilities
• npm run check-formatting --prefix wasm
• npm run build --prefix wasm/worker
• git diff --check

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.58%. Comparing base (c69b9d9) to head (2e72e18).
⚠️ Report is 2 commits behind head on add-fi-finvoice.

Additional details and impacted files

@@               Coverage Diff                @@
##           add-fi-finvoice      #39   +/-   ##
================================================
  Coverage            72.58%   72.58%           
================================================
  Files                   47       47           
  Lines                 1988     1988           
================================================
  Hits                  1443     1443           
  Misses                 465      465           
  Partials                80       80           

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