Add v50 & v51 route inventory documentation (CSV, HTML, Markdown)

[Copilot]

Documents every page route in the v50 and v51 prototypes (300 routes; v50: 143, v51: 157) in three consumable formats under a new docs/ folder.

Routes are extracted from templates in app/views/{v50,v51} that extend layouts/main.html, then cross-referenced with the router.get/post handlers in app/routes/v50.js and app/routes/v51.js. Each route records URL, page title, template, inbound/outbound links, session variables, validation, and conditional logic.

Files added

• docs/v50-v51-routes.md — Markdown tables grouped by version/section; renders natively on GitHub.
• docs/v50-v51-routes.csv — 9-column, 301-row (incl. header) export for spreadsheets.
• docs/v50-v51-routes.html — standalone, dependency-free page with a filter box, v50/v51 toggles, and click-to-sort columns.

Extraction notes

• Session variables and Conditional logic merge each template's own data['…'] / {% if %} usage with the values read and branching performed by the POST -answer handler it submits to — inbound links are the reverse map of outbound href/action targets.
• Validation flags the handful of pages with GOV.UK error markup, a required field, or a JS submit guard; as a Prototype Kit app, the remaining POST handlers only redirect.

Documentation only — no application code is modified.

[SamWooldridgeKainos]

Let's try it out!