Local dev setup; fix mirror volume ownership and a test footgun

Adds docker-compose.override.yml (local-only: publishes the server on
127.0.0.1:8080 and Postgres on 127.0.0.1:55432, crawls on demand) and
docs/LOCAL.md covering the stack, Claude Code registration over both
transports, the CLI, and the test suites.

Two bugs that only running the real container could find:

The mirror volume was root-owned while the container runs as node, so
every file write failed with EACCES. Docker initialises a named volume
from the image directory including its ownership, so the fix is to
create /data/mirror owned by node in the image. This was easy to miss
because the indexer records a per-file failure rather than crashing —
the crawl "succeeded" with 4 skipped. Earlier direct-node testing missed
it entirely by writing to a scratch dir owned by the developer.

The store tests TRUNCATE, and pointing TEST_DATABASE_URL at the dev
database put their fixtures into real data. They now refuse any database
whose name does not contain "test".

Verified against the rebuilt container: 4 files mirrored, image-only PDF
detection firing in the real pipeline, both transports showing
✔ Connected in `claude mcp list`, and a whoami tool call driven end to
end through `claude -p`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Dockerfile

@@ -30,7 +30,14 @@ COPY --from=deps  /app/node_modules ./node_modules
 COPY --from=build /app/dist ./dist
 COPY package.json ./
 
-# node:alpine ships an unprivileged `node` user; the process never writes to disk.
+# The mirror is the one writable path. Creating it in the image with the right
+# owner matters: Docker initialises a new named volume from the image directory,
+# including its ownership, so without this the volume lands root-owned and the
+# unprivileged user gets EACCES on every write — with the failure recorded per
+# file rather than crashing, which makes it easy to miss.
+RUN mkdir -p /data/mirror && chown -R node:node /data
+
+# node:alpine ships an unprivileged `node` user.
 USER node
 
 EXPOSE 8080