feat: add project assignment to issues (fixes #12)

[raegislabs]

Dependencies

None

Resolves

Fixes #12

Summary

Adds --project flag to issue create and issue update commands, enabling complete issue‑project workflow management from the CLI without switching to Linear's web UI.

Motivation

Issue #12 requested the ability to specify project when creating/updating issues. This implements that feature with comprehensive validation and error handling.

Changes

New Features

• --project flag for issue create and issue update commands
  • Accepts project UUID to assign issue to a project
  • Accepts unassigned to remove project assignment
• UUID validation before API calls to provide clear errors early
• Project display in all output formats (table, plaintext, JSON)

Implementation Details

• cmd/issue.go: Flag registration, input building, UUID validation, error handling
• pkg/api/queries.go: GraphQL mutations updated to include project field
• Comprehensive unit tests for flag parsing and validation

Usage Examples

# Create issue assigned to a project
linctl issue create --title "Fix login bug" --team ENG --project 61829105-0c68-43c0-8422-1cb09950cd29

# Assign existing issue to project
linctl issue update ISS-123 --project 61829105-0c68-43c0-8422-1cb09950cd29

# Remove project assignment
linctl issue update ISS-123 --project unassigned

# View project in output
linctl issue get ISS-123  # Shows "Project: linctl"

Validation

• UUID format validation for --project
• unassigned is accepted to remove project assignment
• Clear error messages for invalid UUIDs

Testing

Unit Tests

• Flag registration and help text
• Flag parsing and defaults
• Input validation (UUID format)
• Error scenarios

Smoke/Build

• make test (smoke tests) passing
• make fmt applied

Breaking Changes

None – additive flags only.

Architecture Notes

• Maintains dependency injection and Cobra flag patterns
• Uses explicit flag checks and normalization helper for project input

Checklist

• Tests added and passing
• Code follows existing patterns
• Help text updated and matches behavior
• Manual testing completed
• No breaking changes
• Smoke tests passing

Contributor Checklist (Contributing.md)

• Go 1.22+ environment
• make deps as needed
• make fmt applied
• make test passes (read‑only smoke tests)
• No release actions in this PR (handled on tag per Release Checklist)