Connect guide readers to live waits and saved crossings

[sbc1-code]

Purpose

Turn search visits to BorderPulse guides and crossing pages into a useful path back to current waits, a saved crossing, or a shared guide. This follows the free, ad-supported product direction in #101.

Changes

• Fix the star on crossing detail pages so it saves to the dashboard's existing browser-local favorites list. Show a clear on-device confirmation.
• Add a bilingual guide footer with a current-waits link and WhatsApp/copy sharing. Share URLs use channel-level UTM values only; no person-level referral ID.
• Record blog-to-waits, blog-share, and detail-page favorite-toggle through the existing Umami wrapper.
• Keep Adsterra in its current placement. Its one active native unit and creative quality should be reviewed before adding ads to high-trust guide and crossing pages.

Evidence and review

The latest Umami readout shows most visits enter on guides or crossing pages, while the ad unit is only on the dashboard. Existing favorite-toggle and crossing-share counts are small; this PR is an experiment, not a retention or revenue claim.

git diff --check passed. A direct local Vite build transformed 2,891 modules, then stalled during final bundling on this host and was stopped; the GitHub release check is the build gate for this PR. Automated tests were not run manually in this task.

Public production remains on GitHub Pages. No new package, service, ad unit, account, or recurring cost is added. Production release requires Sebastian's approval.

Related: #101, #102.