repo: move to github.com/tangency-labs/fieldcraft (URLs, updater, Pages)

The updater's release endpoint, docs, README, release notes and the Pages
URL point at the tangency-labs org. App IDs (io.github.jyviko.fieldcraft)
stay unchanged so installed copies keep their identity and settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

docs/updates.md

@@ -7,7 +7,7 @@ each step. The code is `crates/update` (`fieldcraft-update`); the window's side
 ## Checking
 
 The app asks the GitHub Releases API for the latest published release
-(`GET https://api.github.com/repos/jyviko/fieldcraft/releases/latest`; drafts and pre-releases
+(`GET https://api.github.com/repos/tangency-labs/fieldcraft/releases/latest`; drafts and pre-releases
 are never offered) and compares its version with the running one (Semantic Versioning order).
 
 - **At start-up**, at most once a day, when **Check for updates automatically** is on (the