refactor!: packages, paths and app IDs under Halkyon Days' names (ADR 0045, step 3)

Learn's folder is apps/halkyon, Todo's apps/myrmex; every package of
ours takes the prefix halkyone_ (halkyone_halkyon_*, halkyone_myrmex_*,
halkyone_train_*, halkyone_meditate_*, halkyone_app, halkyone_base_* and
the other shared ones; halkyon_oidc_* keeps its name, D11). Halkyon and
Myrmex take the app IDs one.halky.halkyon and one.halky.myrmex (D10);
Train and Meditate keep theirs, while every app's Android namespace,
Kotlin package and method channels move to one.halky. The snaps are
halkyon and myrmex (D17), each built in a clone with its recipe in
place of snap/, as Train's and Todo's were.

Serverpod finds a database's migrations by its module's name, which
changed with the packages':
- each server's new, empty migration ("rename") records itself under
  the new names and deletes the rows under the old ones;
- deploy/redeploy.sh copies each database's record to the new name
  before the migrations (carry_module), so the renamed servers find
  their databases migrated; a copy, never a move, so a deploy failing
  before the migration commits leaves the old rows in place;
- Train and Meditate keep their devices' databases: halkyone_app's
  carryMigrationRecord copies their record before the sync engine
  opens them (openPersonDatabase);
- the client migrations' generated moduleName getters, one line each,
  say the new names: Serverpod's client asserts in debug builds that
  every migration names the module, and create-migration never writes
  a migration's files again.

Train's WorkManager work is enqueued under new names, the former ones
cancelled: the work kept names the workers' former classes.

The release tool: an app's tags of its earlier names count as its
history (legacyTagPrefixes), the shared packages' former paths count
for its version, and every snap is built in a clone (atRoot gone).

The databases, Docker images and Compose project keep their names
until step 5.

BREAKING CHANGE: Halkyon (Learn) and Myrmex (Todo) are new apps to
Android and the Snap Store: installs of app.halkyon.learn and
app.halkyon.todo don't update to them.

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

apps/learn/halkyon_learn_client/lib/migrations/20261020211224692-email-code-purpose/migration.json

@@ -1,33 +0,0 @@
-{
-  "__className__": "serverpod.DatabaseMigration",
-  "actions": [
-    {
-      "__className__": "serverpod.DatabaseMigrationAction",
-      "type": "alterTable",
-      "alterTable": {
-        "__className__": "serverpod.TableMigration",
-        "name": "email_code_request",
-        "schema": "public",
-        "addColumns": [
-          {
-            "__className__": "serverpod.ColumnDefinition",
-            "name": "purpose",
-            "fieldName": "purpose",
-            "columnType": 0,
-            "isNullable": true,
-            "dartType": "protocol:EmailCodePurpose?"
-          }
-        ],
-        "deleteColumns": [],
-        "modifyColumns": [],
-        "addIndexes": [],
-        "deleteIndexes": [],
-        "addForeignKeys": [],
-        "deleteForeignKeys": [],
-        "warnings": []
-      }
-    }
-  ],
-  "warnings": [],
-  "migrationApiVersion": 1
-}