build: the organisation on code.halkyon.app is halkyon-days

ADR 0045, D12, step 1: project-halkyon was renamed halkyon-days, its
repositories keeping their names. Every URL naming it moves along: the
servers' source-code links, which the AGPL requires, and their tests;
the forks in the pubspecs and the lock (appflowy-editor, pure-zstd,
serverpod-offline-sync); the snaps, the F-Droid listings and the
release configurations; the docs. The curator's credit for the
alphabets names the repository by its name since ADR 0015, halkyon,
rather than halkyon_learn. Forgejo redirects the old addresses until
the name is taken again.

ADRs 0015 and 0039 keep the name they were written with, and the local
folders theirs.

halkyon_editor's gen-l10n caches under build/, committed before its
.gitignore named the folder, are no longer tracked.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

snap/snapcraft.yaml

@@ -37,7 +37,7 @@ description: |
 
   Questions and reports: support@halkyon.app
 license: AGPL-3.0-or-later
-source-code: https://code.halkyon.app/project-halkyon/halkyon
+source-code: https://code.halkyon.app/halkyon-days/halkyon
 # The project's, not an instance's: the app works with any instance.
 website: https://halkyon.app/learn
 # No contact or issues: the Store refuses an upload whose links aren't http(s) URLs