fix(chat-service): remove dead runtime path-alias registration crashing prod boot

[ihabkhaled]

Summary

• dist/main.js crashed on every single boot with ReferenceError: __dirname is not defined in ES module scope — chat-service's package.json has "type": "module", and __dirname does not exist in ES modules.
• Root cause: registerTsConfigPaths({ baseUrl: __dirname, ... }) in main.ts was added when this service briefly built with tsgo alone (commit 4e3ce3abc) and needed runtime path-alias resolution. Once tsc-alias was added back to chat-service's build script (matching every other service), it started rewriting @app/*/@common/*/etc. to real relative ./app/*.js imports at build time — making the runtime registration fully redundant. It was never removed, so it kept unconditionally referencing __dirname on every boot.
• Fix: deleted the dead registerTsConfigPaths block and its tsconfig-paths import/dependency. No other service has this pattern (confirmed by repo-wide grep) and no other file in chat-service depends on it.

Release notes

chat-service is broken in production right now — every container crashes immediately on boot. This restores it to booting correctly.

Remaining work

None. This is a minimal, targeted fix — two files changed, nothing else touched.

Test plan

• npx tsgo --noEmit — clean
• npm run lint — 0 errors (71 pre-existing warnings, unrelated to this change)
• npm run test — 1616/1616 tests passing (2 suites hit a pre-existing Windows/Jest path-resolution flake unrelated to this change — verified the flaky files pass 26/26 in isolation)
• npm run build — confirmed dist/main.js contains zero __dirname references and zero bare @app//@common//@infrastructure//@modules/ specifiers (tsc-alias already resolves all of them to relative .js imports)
• Booted dist/main.js directly: it now proceeds through NestJS module resolution and DI all the way to AppConfig.validate(), failing only on missing env vars in this isolated worktree (expected — no .env here). Previously it crashed before a single import even resolved.