Issue #3607991: Add a codebase metrics documentation page
Adds a Codebase metrics documentation page to the mkdocs site: a measured snapshot of the codebase and all of its modules, counted with cloc.
- Lines by language, a production vs test split, code/comment/blank composition, a per-module ranking, a Test suite section (classes and methods by type), and an Architecture surface section (services, plugins, hooks, routes, entities, config schema). Static inline SVG charts, no JavaScript.
- Enables the
tablesMarkdown extension (needed to render the metric tables), adds a nav entry in all three locales (en/fr/es), and addsclocto the cspell word list. Verified withmkdocs build --strict.
The fr/es nav labels are translated ("Métriques du code" / "Métricas del código"); the page content is English (falls back for other locales), consistent with English being the reference language.
Snapshot (3.x): 34,898 lines of code across 485 files; production 22,459 / test 12,439; 118 test classes / 290 methods; 9 modules.