feat: add autocomplete and lookup field types for large datasets

[phmatray]

Summary

Adds two new field types for handling large datasets (100-10K+ rows) that are impractical with static dropdown lists.

Fixes #27

Changes

Core Abstractions (FormCraft/)

• IOptionProvider<TModel, TValue> — async search-based option provider interface
• LookupColumn<TItem> — column definition for lookup table dialogs
• LookupQuery / LookupResult<TItem> — query/result models for server-side pagination
• AsAutocomplete() extensions on FieldBuilder for searchable fields (supports both search functions and IOptionProvider)

Autocomplete Field (FormCraft.ForMudBlazor/)

• MudBlazorAutocompleteFieldComponent — uses MudAutocomplete with server-side search, configurable debounce and min characters
• MudBlazorAutocompleteFieldRenderer — renderer that activates when AutocompleteSearchFunc or AutocompleteOptionProvider attributes are present

Lookup Field (FormCraft.ForMudBlazor/)

• MudBlazorLookupFieldComponent — text field with search icon that opens a MudDialog containing MudTable with pagination, sorting, and filtering
• MudBlazorLookupDialog — reusable dialog component with server-side data, search bar, row selection
• AsLookup() extension with column configuration, value/display selectors, and field mapping callback
• MudBlazorLookupFieldRenderer — renderer that activates when LookupDataProvider attribute is present

Tests

• 10 unit tests for AsAutocomplete() builder extensions (search func, option provider, debounce, min chars, toString, chaining)
• 11 unit tests for AsLookup() builder extensions (data provider, selectors, columns, onItemSelected, defaults, chaining)

Testing

• All 579 existing tests pass (0 failures)
• 21 new unit tests verify builder extension configuration
• Build succeeds with 0 warnings and 0 errors

Discovered Issues

• Phase C (async cascading refresh for DependsOn) is not included — the current sync IFieldDependency interface would need an async variant. Recommend as follow-up issue.