rename: the server is Inkwell — package, env vars, image, compose, export marker

Step 2 of milestone 481. The operator chose a full rename (Scribe note 5071), so
this goes past the display strings into the identities:

- src/thoughtsync → src/inkwell; every import, the Dockerfile and both compose
  commands, alembic env, pyproject
- THOUGHTSYNC_* → INKWELL_* (database URL, secret key, log level, tag/port/bind)
- container data dir /var/thoughtsync → /var/inkwell
- image git.fabledsword.com/bvandeusen/inkwell; Postgres user/db default inkwell;
  CI's integration service follows
- the files the image serves are inkwell.*. fetch-clients.sh still fetches the
  thoughtsync-named release assets, because the lanes that publish them are
  renamed in steps 3 and 4
- exports are written with app "inkwell"

Two deliberate exceptions, both because data rides on them:

- compose volumes are now named explicitly and overridable (INKWELL_DB_VOLUME,
  INKWELL_DATA_VOLUME), so a deployment installed as ThoughtSync points at the
  volumes and DB identity it already has. .env.example says exactly what to set
- import still accepts app "thoughtsync", because exports written before the
  rename are backups. Tested both ways

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_app.py

@@ -1,6 +1,6 @@
 import pytest
 
-from thoughtsync.app import create_app
+from inkwell.app import create_app
 
 
 @pytest.fixture
@@ -61,7 +61,7 @@ async def test_no_version_in_the_environment_reports_unknown(monkeypatch):
     happens to hold, so bumping the packaging version cannot make this pass for the
     wrong reason.
     """
-    from thoughtsync import __version__
+    from inkwell import __version__
 
     monkeypatch.delenv("APP_VERSION", raising=False)
     reported = await reported_version()