fix(docker): drop the duplicate OPENROUTER_API_KEY entry from compose

[Nordalux]

Problem

compose.yaml names OPENROUTER_API_KEY twice under environment::

      # Optional: AI features (SAM, onboarding chat). Without this the setup
      # gate in the app asks for the key, but nothing here would forward it.
      - OPENROUTER_API_KEY=${OPENROUTER_API_KEY:-}
      ...
      # Optional: AI features (SAM, the in-app SEO agent)
      - OPENROUTER_API_KEY=${OPENROUTER_API_KEY:-}
      - OPENROUTER_MODEL=${OPENROUTER_MODEL:-}

This is my fault. #428 had already generalised the passthrough with env_file: .env and listed the key next to OPENROUTER_MODEL. My #152 was merged on top a day later without a rebase, adding a second entry for the same variable.

Nothing is broken: Compose takes the last entry and both resolve to ${OPENROUTER_API_KEY:-}, so the rendered value is unchanged and no warning is emitted. But the duplicate is dead weight, and the comment above my entry now says the opposite of the truth — it claims nothing would forward the key, which stopped being the case the moment env_file landed.

Change

Remove my entry and its stale comment. Keep the one that sits with OPENROUTER_MODEL.

Verification

With a .env containing both variables, docker compose config renders the same values before and after:

      OPENROUTER_API_KEY: sk-or-test
      OPENROUTER_MODEL: some/model

pnpm ci:check passes.

Verified and tested by hand. The description was drafted with AI assistance — I'd rather let the diff do the talking than a long write-up.