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

Cargo.toml

@@ -8,7 +8,7 @@ edition = "2024"
 license = "MIT OR Apache-2.0"
 rust-version = "1.95"
 authors = ["FieldCraft contributors"]
-repository = "https://github.com/jyviko/fieldcraft"
+repository = "https://github.com/tangency-labs/fieldcraft"
 
 [workspace.dependencies]
 # internal