Resolves#38484. This includes a CI job change to make sure we don't
introduce any more env vars that don't get proxied (and thus turned off
outside `--dev`).
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.
- [x] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements)
## Testing
- [x] Added/updated automated tests
Manual QA touched hot paths, but did _not_ manually test every
FLEET_DEV_* environment variable change.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Centralized dev-mode environment management for consistent FLEET_DEV_*
handling and test-friendly overrides.
* Dev-mode allows targeted overrides for certain dev-only configuration
when running with --dev.
* **Chores**
* Migrated environment access to the centralized dev-mode helper across
the codebase.
* Added CI checks to enforce proper usage of FLEET_DEV_* variables.
* **Documentation**
* Added guidance on dev-mode environment variable rules and overrides.
<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Co-authored-by: Victor Lyuboslavsky <2685025+getvictor@users.noreply.github.com>
