[Config] Make the listen address configurable via BIND_ADDRESS

[LarsLaskowski]

📖 Description

Adds a BIND_ADDRESS environment variable so the server can be restricted to a specific network interface (e.g. 127.0.0.1) instead of always binding to all interfaces (0.0.0.0). This closes a gap for deployments that run a reverse proxy on the same host and want the unauthenticated API reachable only via loopback.

• src/server/types.ts: added bindAddress: string to AppConfig.
• src/server/config.ts: reads BIND_ADDRESS, trims it, and falls back to '0.0.0.0' when unset or whitespace-only. No further validation — an unbindable address fails at listen() time.
• src/server/index.ts: passes config.bindAddress to app.listen(...), includes it in the startup log line, and adds a server.on('error', ...) handler so a bad address (e.g. EADDRNOTAVAIL) logs a clear fatal message and exits instead of surfacing as an unhandled 'error' event.
• README.md: documented BIND_ADDRESS in the configuration table.
• deploy/systemd/openhab-log-viewer.service: added a commented example next to the other optional settings.

🎫 Issues

Closes #138

👩‍💻 Reviewer Notes

Default behavior is unchanged (still binds 0.0.0.0 when BIND_ADDRESS is unset). Worth spot-checking that npm run start with BIND_ADDRESS=127.0.0.1 only accepts loopback connections, and that an invalid address (e.g. an address not present on the host) makes startup fail with the new fatal log line instead of hanging.

📑 Test Plan

• src/server/config.test.ts: added a loadConfig bind address parsing suite covering the documented default (0.0.0.0), an explicit BIND_ADDRESS=127.0.0.1, and a whitespace-only value falling back to the default. Also asserted bindAddress in the existing defaults test.
• src/server/routes.test.ts: updated the baseConfig() test fixture to include bindAddress so it satisfies the AppConfig type.
• Ran npm run typecheck, npm test (152/152 passing), and npm run build locally.

✅ Checklist

General

• I have added unit tests for my changes, per UNIT_TESTS.md.
• I have run npm test and npm run typecheck locally and they pass.
• I have updated the project documentation (README, ARCHITECTURE, etc.) to reflect my changes, where applicable.
• I have read the CONTRIBUTING documentation and followed the project's code style and conventions.

Server-specific (src/server)

• I have added or updated a module in src/server (tailer, parser, buffer, routes, SSE hub, config, etc.).
• I have kept src/server/types.ts in sync with src/client/state.ts for any shared payload change (see ARCHITECTURE.md). — N/A, bindAddress is server-only startup config, not part of a client-facing payload.
• I have preserved existing server-side bounds and defaults (buffer/SSE limits, poll interval clamps) unless the change explicitly targets them.

⏭ Next Steps

None.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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