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_flutter/assets/makemeahanzi/ATTRIBUTION.md

@@ -1,23 +0,0 @@
-# Stroke data of Chinese characters
-
-The stroke files in this folder derive from **Make Me a Hanzi**
-(<https://github.com/skishore/makemeahanzi>), its data as of 2018-10-16
-(commit `618dbab`), by Shaunak Kishore:
-
-- the strokes from its `graphics.txt`, derived from the fonts Arphic PL KaitiM
-  GB and Arphic PL UKai, © 1999 Arphic Technology Co., Ltd., distributed under
-  the Arphic Public License (`ARPHICPL.TXT`, unaltered, as it asks);
-- the components from its `dictionary.txt`, derived from the Unihan database
-  (© Unicode, Inc.) and CJKlib, distributed under the GNU Lesser General Public
-  License, version 3 or later (`LGPL.txt`, with Unicode's notice, as Make Me a
-  Hanzi ships it).
-
-They are distributed under the same licences; the app's licence list shows
-both. `halkyon_learn_curator`'s `curate makemeahanzi` writes them (see its
-README), and each file says how and when it was changed (`notice`), as the
-Arphic Public License asks: every stroke is the line Make Me a Hanzi draws
-through its middle (its median), scaled into KanjiVG's 109 × 109 square with
-its y axis pointing down, without the outlines; a character's components are
-the first split of its decomposition (海: 氵, 每). They are an aggregate beside
-the app, never part of its code nor copied into cards: a card names its
-character, and the app draws it from these files.