WEBDEV-9422: Migrate user-service into elements

[jbuckner]

Moves user-service into src/services/user-service/, ported from @internetarchive/user-service 1.0.0 (tag v1.0.0, same commit as npm). All 22 tests came over, converted from mocha and sinon to vitest. It imports the local field-parsers and result-type. UserServiceErrorType is a const object plus a union type because the repo forbids enums. typescript-cookie is a new dependency. The tests still use the npm @internetarchive/local-cache as a dev dependency until WEBDEV-9174 moves it in.

Stacked on #152 (field-parsers). The branch also carries #156 (result-type) until that merges, so this diff includes its files.

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https://claude.ai/code/session_01CjuFdHEwY7MowcqkUxxudu

[github-actions]

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.06%. Comparing base (5640b86) to head (9718828).

Additional details and impacted files

@@                          Coverage Diff                          @@
##           WEBDEV-9418-migrate-field-parsers     #170      +/-   ##
=====================================================================
+ Coverage                              90.85%   91.06%   +0.20%     
=====================================================================
  Files                                    105      110       +5     
  Lines                                   3457     3536      +79     
  Branches                                 835      846      +11     
=====================================================================
+ Hits                                    3141     3220      +79     
  Misses                                   131      131              
  Partials                                 185      185              

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