Automatic spellknown/spellgain null-filling (#12)

Implemented on branches `feature/topdata-row-extensions` in both `toolkit` and `module`.

**Scope Audited**
- Toolkit native topdata collection/build path.
- Project config/effective config validation.
- Module `nwn-tool.yaml` topdata config and topdata README.

**Changes Made**
- Added `topdata.row_extensions` config with `repeat_last` support.
- Added glob dataset matching and build-time row extension for plain native datasets in [native.go](/home/vicky/Projects/nwnee-shadowsoverwestgate/toolkit/internal/topdata/native.go:641).
- Extension copies emitted columns from the highest authored `Level`, increments `Level`, and assigns sequential `id`s through target level.
- Enabled rules for `classes/spellsgained/*` and `classes/spellsknown/*` to level 60 in [nwn-tool.yaml](/home/vicky/Projects/nwnee-shadowsoverwestgate/module/nwn-tool.yaml:90).
- Updated toolkit/module docs.

**Configuration / Compatibility**
- New public config type: `TopDataRowExtensionConfig` in [project.go](/home/vicky/Projects/nwnee-shadowsoverwestgate/toolkit/internal/project/project.go:233).
- Existing behavior is unchanged unless a repo opts into `topdata.row_extensions`.
- Source JSON and lockfiles are not updated for generated extension rows.

**Tests / Validation**
- Added project config tests for loading and validation.
- Added native topdata tests for extension behavior, glob application, preserving manually authored rows, unmatched datasets, and failure cases.
- Ran:
  - `go test ./internal/project ./internal/topdata`
  - `go test ./internal/topdata -run TestBuildNativeKeepsGeneratedIDsStableAcrossRepeatedBuilds`
  - `/tmp/sow-toolkit-rowext config validate` in `module`
  - `/tmp/sow-toolkit-rowext validate-topdata` in `module`
  - `/tmp/sow-toolkit-rowext build-topdata --force`, then inspected generated rows: `cls_spgn_acolyte.2da` now reaches row `59` / level `60`.

**Remaining Notes**
- `validate-topdata` still reports the pre-existing portrait lock warnings for `cotbl/cotbl_` and `lantern/lantern_`.
- `build-topdata --force` briefly rewrote three spellbook JSON files as a side effect; I reverted those, leaving only the intended YAML/docs changes in `module`.

Reviewed-on: https://gitea.westgate.pw/ShadowsOverWestgate/sow-tools/pulls/12
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

internal/project/effective.go

@@ -168,6 +168,7 @@ type EffectiveTopDataConfig struct {
 	ValueEncodings      []TopDataValueEncodingConfig    `json:"value_encodings" yaml:"value_encodings"`
 	ValueDefaults       []TopDataValueDefaultConfig     `json:"value_defaults" yaml:"value_defaults"`
 	RowGeneration       []TopDataRowGenerationConfig    `json:"row_generation" yaml:"row_generation"`
+	RowExtensions       []TopDataRowExtensionConfig     `json:"row_extensions" yaml:"row_extensions"`
 	ClassFeatInjections TopDataClassFeatInjectionConfig `json:"class_feat_injections" yaml:"class_feat_injections"`
 	Wiki                TopDataWikiConfig               `json:"wiki" yaml:"wiki"`
 }
@@ -250,6 +251,7 @@ func (p *Project) EffectiveConfig() EffectiveConfig {
 		ValueEncodings:      cloneTopDataValueEncodings(p.Config.TopData.ValueEncodings),
 		ValueDefaults:       cloneTopDataValueDefaults(p.Config.TopData.ValueDefaults),
 		RowGeneration:       cloneTopDataRowGeneration(p.Config.TopData.RowGeneration),
+		RowExtensions:       cloneTopDataRowExtensions(p.Config.TopData.RowExtensions),
 		ClassFeatInjections: cloneTopDataClassFeatInjections(p.Config.TopData.ClassFeatInjections),
 		Wiki: TopDataWikiConfig{
 			OutputRoot:         defaultString(p.Config.TopData.Wiki.OutputRoot, DefaultTopDataWikiOutputRoot),
@@ -470,6 +472,20 @@ func cloneTopDataRowGeneration(values []TopDataRowGenerationConfig) []TopDataRow
 	return out
 }
 
+func cloneTopDataRowExtensions(values []TopDataRowExtensionConfig) []TopDataRowExtensionConfig {
+	if len(values) == 0 {
+		return nil
+	}
+	out := make([]TopDataRowExtensionConfig, len(values))
+	copy(out, values)
+	for index := range out {
+		out[index].Dataset = filepath.ToSlash(strings.TrimSpace(out[index].Dataset))
+		out[index].Mode = strings.TrimSpace(out[index].Mode)
+		out[index].LevelColumn = strings.TrimSpace(out[index].LevelColumn)
+	}
+	return out
+}
+
 func cloneTopDataClassFeatInjections(value TopDataClassFeatInjectionConfig) TopDataClassFeatInjectionConfig {
 	out := TopDataClassFeatInjectionConfig{
 		GlobalFeats:           slices.Clone(value.GlobalFeats),