fix(file-service): restore configured S3 uploads

[devin-ai-integration]

Summary

• Symptom / blast radius: file uploads return 500 storage_error for every user running the affected file-service image because S3 writes are redirected away from the configured bucket.
• Root cause (config/env): the production image defaults FILE_UPLOAD_ALWAYS_FAIL=true; upload_file therefore selects otterworks-files-chaos-nonexistent instead of S3_BUCKET.
• Fix: remove the image-level default while preserving explicit runtime overrides, and add a regression guard that rejects truthy Docker ENV defaults in assignment, legacy, multi-variable, quoted, and continued forms.
• Verification: cargo test (26 passed), cargo fmt --check, cargo clippy --all-targets -- -D warnings, and green CI. A rebuilt image has no baked upload-failure default; the browser upload returned HTTP 201, LocalStack S3 gained one 77-byte object byte-identical to the source, and the file loaded through Search and its detail/download flow. The explicit runtime override still reproduces the failure without writing an object. Screen recording.

Independent incident run; compare with #266. This implementation keeps the runtime failure switch available but prevents the production image from enabling it by default.

Unrelated follow-up: the Files grid fetches only its first 50 results and sorts that page client-side, so a just-uploaded file in this large seeded drive is visible through Search but not the grid.

Link to Devin session: https://app.devin.ai/sessions/6c565ca90fd4476dbe269672de1bd6ba

---

Devin Review

Status	Commit
⚪ Not started	—

Run Devin Review

---

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

Devin Review found 2 potential issues.