Move tavolo-app under packages/ for a uniform monorepo layout

Relocate the composition root (app, config, static, logging_config,
aerich_config) from server/src/tavolo/ to
packages/tavolo-app/src/tavolo/, with its own pyproject.toml and README
like the sibling distributions. Module paths and the granian entrypoint
are unchanged.

server/pyproject.toml remains as a tooling shim ([tool.aerich] next to
./migrations, [tool.mypy] for runs from server/); the Dockerfile installs
all three distributions from ./packages. Verified: all suites green,
mypy clean per package, aerich resolves the moved config identically,
wheel builds.

server/Dockerfile

@@ -55,14 +55,16 @@ RUN --mount=type=cache,target=/root/.cache/pip \
  && /opt/venv/bin/pip install --upgrade pip \
  && /opt/venv/bin/pip install -r requirements.txt
 
-COPY server/pyproject.toml server/README.md ./
-COPY server/src/ ./src/
-# Sibling distributions, installed from the local tree (PEP 420 namespace
-# packages sharing the `tavolo` namespace with the app above). --no-deps:
-# every third-party dependency is already pinned in requirements.txt.
+# The three sibling distributions, installed from the local tree (PEP 420
+# namespace packages sharing the `tavolo` namespace). --no-deps: every
+# third-party dependency is already pinned in requirements.txt.
 COPY server/packages/ ./packages/
 RUN --mount=type=cache,target=/root/.cache/pip \
-    /opt/venv/bin/pip install --no-deps ./packages/tavolo-platform ./packages/tavolo-scopone .
+    /opt/venv/bin/pip install --no-deps ./packages/tavolo-platform ./packages/tavolo-scopone ./packages/tavolo-app
+# server/pyproject.toml only carries the [tool.aerich] section (the
+# db-migrate compose service runs `aerich upgrade` with working_dir=/app,
+# next to ./migrations).
+COPY server/pyproject.toml ./
 # aerich migration files are a release artifact: the db-migrate compose
 # service runs `aerich upgrade` from this image before the app starts.
 COPY server/migrations/ ./migrations/