fix: change appname to neoirc, default DB to /var/lib/neoirc/state.db (#45)

## Changes

- Change `Appname` from `"chat"` to `"neoirc"` in `cmd/chatd/main.go`
- Change default `DBURL` from `file:./data.db?_journal_mode=WAL` to `file:///var/lib/neoirc/state.db?_journal_mode=WAL` in both `internal/config/config.go` and the `internal/db/db.go` fallback
- Create `/var/lib/neoirc/` directory in Dockerfile with proper ownership for the `chat` user
- Update README.md to reflect new defaults (DBURL table, `.env` example, docker run example, SQLite backup/location docs)
- Remove stale `data.db` reference from Makefile `clean` target

The DB path remains configurable via the `DBURL` environment variable. No Go packages were renamed.

Closes #44

Co-authored-by: clawbot <clawbot@noreply.eeqj.de>
Reviewed-on: #45
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

Dockerfile

@@ -33,7 +33,9 @@ RUN CGO_ENABLED=0 go build -trimpath -ldflags="-s -w" -o /chat-cli ./cmd/chat-cl
 # alpine:3.21, 2026-02-26
 FROM alpine@sha256:c3f8e73fdb79deaebaa2037150150191b9dcbfba68b4a46d70103204c53f4709
 RUN apk add --no-cache ca-certificates \
-    && addgroup -S chat && adduser -S chat -G chat
+    && addgroup -S chat && adduser -S chat -G chat \
+    && mkdir -p /var/lib/neoirc \
+    && chown chat:chat /var/lib/neoirc
 COPY --from=builder /chatd /usr/local/bin/chatd
 
 USER chat