refactor: establish sites/brc-analytics landing zone and migrate calendarview

[frano-m]

Part of the site-separation effort (#1246 / #1417).

Goal

Start gently relocating BRC-owned views into sites/brc-analytics/ under the existing single root build — no changes to build scripts, sync-api, next build, or site-config. This pre-positions BRC code for the eventual per-site apps without committing to independent builds yet.

Scope (pilot: CalendarView)

• Add a sites/brc-analytics/* → @brc/* path alias to root tsconfig.json.
• Move app/views/CalendarView/ → sites/brc-analytics/views/CalendarView/ (flattened — constants.ts at the view root).
• Repoint pages/calendar to @brc/views/CalendarView/calendarView.

Why this works without build/config churn

• @/* and @site-config/* are repo-root-relative, so the view's existing @/components/* imports resolve unchanged after the move.
• Views live only in the tsc + Next/webpack graph, both of which honor tsconfig path aliases — so a plain alias suffices (no workspace-package needed).

Known boundary (not in scope)

routes/constants.ts (site page-routes) can not ride the @brc alias — it's imported by GA2's site-config and by Playwright e2e, neither of which resolve tsconfig aliases. It stays at root for now; relocating it later needs a Playwright-reachable home (workspace package or relative path), not the alias.

Acceptance

• pages/calendar renders identically (verified via build:local + serve).
• tsc / eslint / prettier / unit tests / build green.