Reject NUL characters in the Lidarr root folder with a 400

[rowkav09]

Same class as #215 and #216. rootFolderPath from POST /api/v1/settings/lidarr is stored in Postgres, which cannot hold NUL, so a payload containing \u0000 passed validation, contacted the Lidarr server, and then failed in the upsert with a 500. The schema now refuses NUL, so the request gets the existing 400 INVALID_REQUEST before any network call or query. Test: on main the request is not rejected with 400 and reaches the network call; with the change it answers 400 and neither fetch nor the database is touched. This route had no api test before. Behaviour change: invalid payload returns 400 instead of 500.

[rowkav09]

APPROVE at head 240e8d4.

Checked out the head (origin/main is an ancestor, stacked on #216). rootFolderPath now goes through the shared noNul refine, and both routes that parse LidarrConnectionRequestSchema (save at server.ts:1070 and test at :1096) pick it up. Full suite 366/366 passes, tsc is clean. Fail-first: with main's lidarr.ts under the PR's test, the new NUL test fails (400 expected); with the change it passes.

CI at this head when I looked: CodeFactor and ghostdeps succeeded, "Verify TypeScript workspace" was still in progress, so not CI-green yet. Same-account review.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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