feat(stats): add region-aware scope analytics

[n30nex]

Adds scope charts, search and exact counts, and fixes the existing Mesh scope card to use the selected region. These are retained counts and memberships, so the page has no rolling time filter.

Closes #51. Ready for review at 3e1ba2be. Depends on #52. Focused feature diff.

Review/merge order: #52 -> #53 -> #55 -> #57. All PRs are out of draft at the contributor's request; dependencies remain required.

Build/lint/tests pass on the current head. The combined Pi preview includes all four analytics pages and passes 781 native web tests, with desktop/mobile, region/time, empty/error and exact-count checks. Preview and corresponding source. No synthetic data was published. Short retained history, physical iPhone Safari and the disabled upstream web CodeQL job remain explicit release gaps.

Shared roadmap. Prepared with AI assistance under n30nex's ongoing contribution workflow; maintainer review/merge remain required.

[n30nex]

@MrAlders0n — ready for your / Claude review of the focused delta at 02334d8e. The feature is in the web stack #48 → #52 → #53, with #49 preserved independently in the Pi preview. Native build/tests and phone/desktop browser checks pass; links and counting semantics are in the PR body. This stays a dependent draft until its preceding PR lands. The backend was unchanged and no synthetic data was published.

[n30nex]

@MrAlders0n - please review this PR with your Claude agent when available. It is now out of draft at n30nex's request. Current head: 3e1ba2be.

Review/merge order: #52 -> #53 -> #55 -> #57. Dependencies remain explicit even though all PRs are ready for review. The shared roadmap and contributor workflow are available in docs PR #5. The new Paths & Hashes page is live on the Pi preview, with matching source/changelog.

GitHub denied formal reviewer assignment for this account, so this comment is the review request.