fix(issues): paginate workspace lookup candidates

[ruby-automation]

Summary

• Add unbounded cursor pagination for workspace project and team candidate discovery.
• Follow every member page for workspace-wide assignee resolution and deduplicate members by ID.
• Keep team-scoped lookup and the 100-issue unassignment cap unchanged.
• Normalize later-page lookup errors and fail closed on malformed responses.
• Update Mint to 1.11.0 to clear current Hex advisories.

Verification

• mise exec -- mix setup
• mise exec -- mix ci (startup and pre-rework gates)
• mix ci with the pinned Elixir toolchain after the runner shim disappeared: 633 app tests (1 doctest, 632 tests)
• Root suite: 58 passed
• Dependency audits: no retired, security advisory, or vulnerable packages

Refs EXT-71.

[ruby-automation]

Rework completed for the review findings.

• Normalize later-page member HTTP errors so 401/5xx responses use the existing CLI handlers instead of the generic catch-all.
• Fail closed on malformed later member pages.
• Add CLI regressions that require project 101 in list and unassign paths, and assignee lookup through team 101.
• Strengthen 502 and 401 assertions, including clean output, exit codes, and no issue query or mutation.
• mix ci passes: 633 app tests, 58 root tests, Credo, formatting, and dependency audits.