docs: one repository for every app and shared package (ADR 0015)

The root AGENTS.md holds what applies to every app and package (how
work is done, Serverpod, checks with Melos and the tools, CI); Learn's
own is apps/learn/AGENTS.md, Todo's a note that it is still the
scaffold. The root README introduces the project, Learn's moves to its
folder; LICENSE.md says which licence covers which directory, Todo's
packages unlicensed until decided; one CONTRIBUTING.md. ADR 0015
records the decision; ADR 0014 and 0003 note what moved.

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

docs/adr/0014-halkyon-base-module.md

@@ -2,6 +2,11 @@
 
 - **Status:** accepted
 - **Date:** 2026-10-19
+- **Amended by:** [ADR 0015](0015-one-repository.md) (2026-10-19): halkyon_shared's packages
+  now live in this repository's `packages/`, which the apps take by path. Where this record
+  says the module, `halkyon_ui` and `halkyon_app` are pinned by git to signed commits of
+  halkyon_shared's main, read: taken by path, a change to the module and its hosts one
+  commit.
 
 ## Context