fix(#638): Add custom field type discovery support

[ryancheley]

Summary

Implement dynamic field type discovery to support all YouTrack custom field types, not just Enum types. The CLI now automatically detects field types from project configuration with intelligent fallback behavior.

Previously, the --custom-field option only worked with Enum fields because it hardcoded all custom fields as SingleEnumIssueCustomField. Non-enum fields (Text, Integer, Date, User, Version, Build, etc.) would fail with type mismatch errors.

Now, the CLI queries the project's custom field configuration to determine the actual field type and uses the appropriate field creation method. If type discovery fails, it gracefully falls back to enum type with a helpful warning.

Changes

Custom Field Manager (youtrack_cli/custom_field_manager.py)

• Added create_simple_field() for integer/float custom fields
• Added create_date_field() for date custom fields
• Added create_single_version_field() for version fields
• Added create_single_build_field() for build fields
• Added create_field_by_type() polymorphic dispatcher that creates the appropriate field type based on discovered information

Project Service (youtrack_cli/services/projects.py)

• Added discover_custom_field() method that:
  • Queries all project custom fields
  • Finds the field by name (case-insensitive)
  • Determines the issue field type from project field type
  • Extracts bundle element type information
  • Caches results for performance
• Added _project_to_issue_field_type() mapping to convert between project and issue field type constants

Issue Service (youtrack_cli/services/issues.py)

• Updated create_issue() to use field type discovery instead of hardcoding enum types
• Updated update_issue() with identical field discovery logic
• Added graceful fallback with warning logs when discovery fails
• Maintains full backward compatibility with existing enum field handling

Documentation (docs/commands/issues.rst)

• Added comprehensive custom fields section with:
  • List of all supported field types
  • Explanation of automatic type detection
  • Practical examples for each field type (enum, text, integer, user)
• Updated both create and update command documentation

Changelog (CHANGELOG.md)

• Documented fix with details about type discovery and fallback behavior

Supported Field Types

The --custom-field option now supports all YouTrack field types:

• Enum (single/multi) - Team=Backend
• Text - Notes=Implementation notes
• Simple (integer/float) - StoryPoints=5
• User (single/multi) - Reviewer=john.doe
• Version (single/multi) - FixVersion=1.0
• Build (single/multi) - Build=Release-123
• Date/DateTime - DueDate=1234567890000
• Period - Time period fields
• State - Status/workflow state fields

Technical Details

Type Discovery Pattern

Follows the established pattern from discover_state_field() method:

1. Check cache first for performance
2. Query project custom fields API
3. Find field by name (case-insensitive)
4. Get detailed field information including bundle type
5. Extract and store field metadata
6. Cache results for subsequent operations

Fallback Behavior

If field type discovery fails for any reason:

• Logs a warning message with the error
• Falls back to creating an enum field (safest default)
• Continues processing other fields
• Does not stop the entire operation

Performance

• Field type information is cached after first discovery
• Subsequent operations for the same field use cached data
• No performance regression for enum fields

Testing

• All 1359 existing tests pass
• All pre-commit checks pass (ruff, ty, pydocstyle, pytest)
• Test coverage maintained at 60%

Fixes #638