feat: Add example pages and stacked-tables partial

[AdamJ]

Description of changes

• Introduce example pages and a reusable stacked-tables partial for component demos.
• Adds docs/examples and docs/pages/examples HTML, new Nunjucks include/partial (src/_includes/examples.njk, src/_partials/stacked-tables.njk) and example page sources (src/pages/examples/examples.json, src/pages/examples/index.md).
• Update project cost views to wrap several to-date totals with links to /casWOW/costs/to-date-costs/ (docs/costs/project-costs/index.html and src/_includes/project-costs.njk) and update pages index (src/pages/pages.json).
• These changes provide developer-facing example content and a shared table partial for reuse.

PR checklist

Please check the boxes that apply before requesting review.

• I ran the site locally (pnpm show) and verified the changed pages
• I ran the production build (pnpm css && pnpm build) and checked docs/ output
• I updated or copied vendor assets using the package.json copy scripts if required (pnpm copy-css|copy-js|copy-fa|copy-cas)
• If this change depends on caswow.library, I documented whether it was linked with npm link or included in CI
• I verified there are no uncaught exceptions in the browser console (common: dialog script in base.njk)
• I added notes in this PR about any assumptions made (missing vendor files, local links, env variables)

Optional guidance for reviewers:

• For layout or JS changes, preview the affected page(s) in docs/ after a prod build.
• If vendor files were updated, confirm dependencies/ and docs/ contain the expected updated files.