feat: feature flag guard provision version to allow rolling update

[dobrac]

This should allow to gradually roll provision script update without invalidating all templates at the same time.

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Note

Use a build-provision-version feature flag in base layer hashing to enable gradual provision script rollouts, wiring feature flags and contexts through the build pipeline.

• Build Pipeline / Orchestrator:
  • Pass featureFlags into build.NewBuilder and base.New(...); store on Builder/BaseBuilder.
  • Use int flag BuildProvisionVersion in base.Hash(ctx, ...) to select provision version for cache keys; include TemplateContext and TeamContext.
  • Update BuilderPhase.Hash signature to Hash(ctx, ...) and adjust implementations in base, finalize, steps, and user.
• Feature Flags:
  • Add TemplateKind and TemplateContext; add BuildProvisionVersion int flag.
  • Split team contexts: new TeamContextWithName(teamID, teamName) and TeamContext(teamID); API middleware now uses TeamContextWithName.
• Wiring/Infra:
  • Propagate featureFlags client through template server, CLI build tool, benchmarks, and orchestrator startup.

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