feat: schema field default, min/max, and pattern

[careck]

Summary

• default_value: on any field — sets the initial value for new notes instead of zero-values (Rhai key: default_value since default is reserved in Rhai)
• min: / max: on number fields — declarative range validation without writing a validate closure
• pattern: on text/email fields — regex validation shortcut

Built-in validation runs before closure-based validate, and both can produce errors. Frontend inputs get HTML min/max/pattern attributes for immediate browser hints, plus server-side validation on blur via IPC.

Closes #122

Changes

• FieldDefinition struct: 4 new fields (default_value, min_value, max_value, pattern)
• default_fields(): respects script-specified defaults via dynamic_to_field_value()
• validate_field() / validate_fields(): run built-in checks (min/max/pattern) before closure
• FieldDefInfo Tauri bridge: carries minValue, maxValue, pattern, hasDefault to frontend
• TS FieldDefinition: new optional fields
• FieldEditor.tsx: HTML min/max/pattern attributes on inputs
• useNoteForm.ts: triggers blur validation for fields with built-in constraints
• i18n: validation error keys added to all 7 locales
• 20 new tests covering defaults, range validation, pattern validation, and combined scenarios

Rhai script usage

schema("Product", #{
    fields: [
        #{ name: "price", type: "number", min: 0, max: 99999 },
        #{ name: "sku", type: "text", pattern: "^[A-Z]{2}-\\d{4}$" },
        #{ name: "status", type: "select", options: ["Draft", "Active"], default_value: "Draft" },
        #{ name: "stock", type: "number", default_value: 0, min: 0 },
    ]
});

Test plan

• cargo test -p krillnotes-core — 699 tests pass (20 new)
• cargo clippy -p krillnotes-core — clean
• cargo fmt --check — clean
• npx tsc --noEmit — clean
• Manual: create a schema with min/max number field, verify inline error on blur
• Manual: create a schema with pattern text field, verify regex validation
• Manual: create a schema with default_value, verify new notes pre-populate