Add Docker deploy and Gitea Actions CI, plus a local testing guide

Dockerfile/docker-compose.yml mirror keep's pattern — same
better-sqlite3 native-addon build story, same pull_policy: always +
named volume for the SQLite DB so redeploys don't lose captured
articles. Gitea Actions workflow builds and pushes to the Gitea
container registry on push to main (needs a TKNTKN repo secret, same
as keep/wisp/npm-statuspage).

TESTING.md is the step-by-step for running the server + loading the
extension unpacked, written up from what was actually verified
end-to-end in the previous session.

Verified: image builds, server starts and responds inside the
container, capture works, and data survives a container restart.

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

docker-compose.yml

@@ -0,0 +1,15 @@
+services:
+  app:
+    image: ${IMAGE}
+    container_name: stash
+    restart: unless-stopped
+    pull_policy: always
+    ports:
+      - "${HOST_PORT:-3070}:3070"
+    volumes:
+      # Named volume, not a bind mount — the SQLite DB holding captured
+      # articles and tokens must survive redeploys.
+      - stash-data:/app/data
+
+volumes:
+  stash-data: