feat(schemas): schema-driven slim fields on users (Phase 3b, DOT-560)

[ichoosetoaccept]

Sibling of DOT-558 (Phase 3a). Extends the schema-driven slim-fields
pattern (canonical: PR #109, PR #110) to the users domain — the one
piece Phase 3a deferred because the slim shape needed a privacy-aware
design pass.

Slim shape: identity-only — id, username, name, state, avatar_url,
web_url, bot. Seven fields. Always safe to expose for any user.
Privacy-sensitive fields (email, last_sign_in_at, is_admin,
two_factor_enabled, confirmed_at, current_sign_in_at, private_profile,
last_activity_on, theme_id, color_scheme_id, projects_limit, external)
are excluded by default; opt back in via fields:'all' or explicit pick.
A dedicated test pins the privacy guardrail so future expansions of
UserSlimShape can't accidentally leak those fields.

Phase-1 gaps closed along the way:

• src/schemas/users.ts: GitLabUserListSchema didn't exist; add it.
• src/tools/users.ts: get_users and search_users were never wrapped
  with parseGitLabResponse; wrap them now (a prerequisite for typed
  slim defaults to project from).

Wires four user-returning tools with fields + projection:

• get_current_user (already parse-wrapped, just adds fields+project)
• get_user (already parse-wrapped, just adds fields+project)
• get_users (newly parse-wrapped, per-username map slimmed element-wise)
• search_users (newly parse-wrapped, list slimmed)

Out of scope: list_events, get_project_events, upload_markdown,
download_attachment, health_check — they live in users.ts for
organizational convenience but don't return user-shaped data.

Tests:

• tests/schemas/users.test.ts: slim-schema parse, USER_SLIM_FIELDS
  allow-list invariant, projectField allow-list at runtime,
  privacy guardrail (USER_SLIM_FIELDS does NOT contain email /
  is_admin / two_factor_enabled / etc.), separate test that
  projectField actually drops those fields on a populated current-user
  fixture, GitLabUserListSchema parse, token-budget regression.
• tests/users.test.ts: default / fields:'all' / custom-pick handler
  tests for each of the four tools (12+ cases). get_current_user and
  get_user tests specifically verify privacy fields absent by default
  and present under fields:'all'. search_users test confirms fields
  is not forwarded to GitLab as a query string.

README "Field Projection" section extended to list the four user
endpoints.

Note

Add schema-driven slim field projection to all four user-returning tools

• Adds UserSlimShape, GitLabUserSlimSchema, USER_SLIM_FIELDS, and GitLabUserListSchema to src/schemas/users.ts, exporting a privacy-aware 7-field identity shape (id, username, name, state, avatar_url, web_url, bot).
• Wires fields: fieldsParam("user").optional() and projectField/projectFields into get_current_user, get_user, get_users, and search_users; all four now return the slim shape by default.
• Wraps get_users and search_users with parseGitLabResponse(GitLabUserListSchema, ...) for the first time, closing a Phase-1 gap.
• Privacy-sensitive fields (email, is_admin, two_factor_enabled, last_sign_in_at, etc.) are excluded from the default output and only returned when fields="all" or explicitly requested.
• Behavioral Change: all four user tools now return a reduced field set by default; callers relying on full payloads must pass fields="all".

🖇️ Linked Issues

Completes DOT-560, which tracks Phase 3b of the response-schema initiative for the users domain. Part of the broader DOT-555 initiative to introduce Zod response schemas as a token-efficiency primitive.

^{Macroscope summarized f10b61c.}

[ichoosetoaccept]

This change is part of the following stack:

• feat(schemas): schema-driven slim fields on users (Phase 3b, DOT-560) #111 ◀

_{Change managed by git-spice.}

[linear-code]

DOT-560

[macroscopeapp]

Approvability

Verdict: Needs human review

This PR changes the default response shape of 4 user endpoints to return fewer fields (excluding privacy-sensitive data). While backwards-compatible via fields: 'all', this runtime behavior change affecting multiple endpoints warrants human verification that downstream consumers are prepared for the modified defaults.

^{You can customize Macroscope's approvability policy. Learn more.}

[github-actions]

🎉 This PR is included in version 2.32.0 🎉

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