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>

packages/halkyon_app/README.md

@@ -28,7 +28,7 @@ Written as the apps are: Dart 3.13's primary constructors, Material from
   have their own, such as Scotland; else the country's). Countries are named
   by the app's `CountryNames`, subdivisions by Unicode CLDR's names in English
   and German, which come with the package (`AssetSubdivisionNames`; the
-  workspace's `tool/subdivision_names.py` writes them).
+  package's `tool/subdivision_names.py` writes them).
 - **Gates** (`lib/src/app/`): `InstanceGate` opens the app's dependencies on
   the instance in use (`AppDependencies`, handed down by `AppScope`), anew on
   a switch, the previous ones closed first; `SessionGate` keeps a person
@@ -57,17 +57,13 @@ Written as the apps are: Dart 3.13's primary constructors, Material from
 
 1. **The server** includes `halkyon_base` with the nickname `base` (its
    README), so the app's generated client has `client.modules.base`.
-2. **Depend on it** by git, pinned to a signed commit of halkyon_shared's
-   main, as `halkyon_ui` (whose README shows the `pubspec_overrides.yaml` for
-   working on both at once):
+2. **Depend on it** by path, within the repository's workspace, as on
+   `halkyon_ui`:
 
    ```yaml
    dependencies:
      halkyon_app:
-       git:
-         url: https://code.halkyon.app/project-halkyon/halkyon_shared.git
-         path: packages/halkyon_app
-         ref: <signed commit>
+       path: ../../../packages/halkyon_app
    ```
 
 3. **Texts**: add `HalkyonAppLocalizations.delegate` to every `MaterialApp`'s

packages/halkyon_base_server/README.md

@@ -33,15 +33,13 @@ Endpoints, under the nickname `base` in a host's client (`client.base.emailCode`
 
 ## Taking it into a host
 
-1. Depend on both packages, pinned to a signed commit of `halkyon_shared`:
+1. Depend on both packages by path, within the repository's workspace (an app's
+   packages sit in `apps/<app>/`):
 
    ```yaml
    # the server's pubspec.yaml
    halkyon_base_server:
-     git:
-       url: https://code.halkyon.app/project-halkyon/halkyon_shared.git
-       path: packages/halkyon_base_server
-       ref: <signed commit>
+     path: ../../../packages/halkyon_base_server
    # the client's pubspec.yaml: the same with halkyon_base_client
    ```
 

packages/halkyon_ui/README.md

@@ -42,29 +42,15 @@ What belongs to one app stays in it: its own colours (an extension passed to
 
 ## Using it in an app
 
-Depend on it by git, pinned to a signed commit, as the apps pin their forks:
+Depend on it by path, within the repository's workspace (an app's packages sit in
+`apps/<app>/`), so a change to the package and to the apps using it is one commit:
 
 ```yaml
 dependencies:
   halkyon_ui:
-    git:
-      url: https://code.halkyon.app/project-halkyon/halkyon_shared.git
-      path: packages/halkyon_ui
-      ref: <signed commit>
+    path: ../../../packages/halkyon_ui
 ```
 
-While changing both at once, point the app at a local checkout with a
-git-ignored `pubspec_overrides.yaml` beside the app's workspace root:
-
-```yaml
-dependency_overrides:
-  halkyon_ui:
-    path: ../halkyon_shared/packages/halkyon_ui
-```
-
-The lockfile then records the path: never commit it so, as CI has no such
-folder.
-
 Then set the app up as `example/lib/main.dart` does:
 
 ```dart
@@ -95,7 +81,7 @@ fallback); `halkyon_ui_de.arb` German, informal "du"; `halkyon_ui_en_US.arb`
 only what American English spells differently; `halkyon_ui_en_GB.arb` empty. A
 new text goes into the template and German together (`test/l10n/` fails
 otherwise). `flutter pub get` writes `lib/l10n/halkyon_ui_localizations*.dart`,
-which are committed (apps take the package by git) and never edited or
+which are committed and never edited or
 formatted by hand.
 
 ## Checks