feat(frontend): feature flag compute (#5098)

# Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
- [ ] This change requires a documentation update

## How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my feature works
- [ ] New and existing unit tests pass locally with my changes

Author: abcxff

.claude/reference/feature-flags.md

@@ -28,12 +28,13 @@ if (features.platform) {
 | `acl` | Engine enforces token auth on the public endpoint. Implied by `platform`; set independently for enterprise. |
 | `billing` | Billing UI. |
 | `captcha` | Turnstile captcha on auth forms. Requires `auth`. |
+| `compute` | Rivet Compute (managed pool) UI: namespace deployments + logs sidebar links and routes, actor-details deployment-logs tab, and the Rivet provider option in onboarding / Add Provider. Requires `platform`. |
 | `support` | Support/help affordances. |
 | `branding` | Rivet branding chrome. |
 | `datacenter` | Datacenter-related UI. |
 | `danger-zone` | Destructive settings actions (`features.dangerZone`). |
 
-Deployment flavors map to flag sets roughly as: **cloud** = all on; **OSS** = `auth`/`platform`/`acl` off; **enterprise** = `acl` on, `auth`/`platform` off (engine enforces auth without a login UI). Do not treat `platform`/`auth` as "engine requires credentials" — that is `acl`.
+Deployment flavors map to flag sets roughly as: **cloud** = all on; **OSS** = `auth`/`platform`/`acl` off; **enterprise** = `acl` on, `auth`/`platform` off (engine enforces auth without a login UI). Do not treat `platform`/`auth` as "engine requires credentials" — that is `acl`. **`compute` is opt-in even on cloud** — each Railway service adds it to `VITE_FEATURE_FLAGS` per-environment (e.g. staging on, prod off) rather than inheriting the cloud default-on set.
 
 ## When to add a new flag