Canonical Wiki Paths Enforcement (#6)

### Summary
- Change generated topdata wiki links to target public wiki namespace and canonical slug paths.
- Add generated public path metadata to wiki page generation and page-index output.
- Add YAML-driven generated slug overrides and public-target collision validation.

### Details
- Generated relation links now render public targets such as:
  - `[[feat/hardiness-vs-enchantments|Hardiness vs. Enchantments]]`
  - `[[feat/favored-enemy-elves|Favored Enemy: Elves]]`
- Topdata page IDs remain the internal identity for output layout, managed markers, deploy state, and bookkeeping.
- Generated managed markers now include the effective public slug:
  - `<!-- sow-topdata-wiki:page=... wiki_slug=... -->`
- Page-index entries now include:
  - `public_slug`
  - `public_target`
- Added parsing and validation for `page_paths.slug_overrides` from `topdata/wiki/wiki.yaml`.
- Generated public targets are validated for duplicate namespace-local collisions.
- Table link helpers now derive public targets from target page titles when available, so display aliases do not accidentally change link destinations.

### Tests
- Added and updated coverage for:
  - public target rendering
  - marker `wiki_slug` output
  - page-index public metadata
  - duplicate generated public target rejection
  - slug override parsing and validation
  - override-driven target selection
  - target title slugging independent of display labels

### Validation
- `go test ./...`
- `gofmt -w` on changed Go files
- `./build-tool.sh`
- `git diff --check`

Reviewed-on: https://gitea.westgate.pw/ShadowsOverWestgate/sow-tools/pulls/6
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

internal/topdata/wiki_page_paths.go

@@ -0,0 +1,74 @@
+package topdata
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+type wikiPagePathDocument struct {
+	PagePaths wikiPagePaths `json:"page_paths" yaml:"page_paths"`
+}
+
+type wikiPagePaths struct {
+	SlugOverrides []wikiPageSlugOverride `json:"slug_overrides" yaml:"slug_overrides"`
+}
+
+type wikiPageSlugOverride struct {
+	PageID string `json:"page_id" yaml:"page_id"`
+	Slug   string `json:"slug" yaml:"slug"`
+}
+
+func loadWikiPagePathDeclarations(path string) (map[string]string, error) {
+	raw, err := os.ReadFile(path)
+	if os.IsNotExist(err) {
+		return map[string]string{}, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return parseWikiPagePathDeclarations(raw, path)
+}
+
+func parseWikiPagePathDeclarations(raw []byte, path string) (map[string]string, error) {
+	var doc wikiPagePathDocument
+	if err := yaml.Unmarshal(raw, &doc); err != nil {
+		return nil, fmt.Errorf("parse wiki page paths %s: %w", path, err)
+	}
+	overrides := map[string]string{}
+	for _, override := range doc.PagePaths.SlugOverrides {
+		pageID := strings.TrimSpace(override.PageID)
+		slug := strings.TrimSpace(override.Slug)
+		if pageID == "" {
+			return nil, fmt.Errorf("parse wiki page paths %s: slug override has empty page_id", path)
+		}
+		if !isCanonicalWikiSlug(slug) {
+			return nil, fmt.Errorf("parse wiki page paths %s: page_id %q has invalid slug %q", path, pageID, override.Slug)
+		}
+		if _, ok := overrides[pageID]; ok {
+			return nil, fmt.Errorf("parse wiki page paths %s: duplicate page_id %q", path, pageID)
+		}
+		overrides[pageID] = slug
+	}
+	return overrides, nil
+}
+
+func isCanonicalWikiSlug(value string) bool {
+	if value == "" || value != strings.ToLower(value) {
+		return false
+	}
+	parts := strings.Split(value, "-")
+	for _, part := range parts {
+		if part == "" {
+			return false
+		}
+		for _, r := range part {
+			if !((r >= 'a' && r <= 'z') || (r >= '0' && r <= '9')) {
+				return false
+			}
+		}
+	}
+	return true
+}