Re-tune onboarding model recommendations for the base-model tiers

[FuJacob]

Summary

The onboarding recommender's warning copy and memory thresholds were sized for the old ~3–5 GB instruct models. The base-model tiers are much smaller — quick 0.8 GB, everyday 1.4 GB, powerful 2.6 GB — so the Powerful disable floor of 10 GB wrongly excluded stock 8 GB Macs that can comfortably run a 2.6 GB model. This lowers that floor to 8 GB and derives the "~X GB" sizes in the copy from the catalog so they can't drift.

Validation

xcodebuild -project Cotabby.xcodeproj -scheme Cotabby -destination 'platform=macOS' \
  build-for-testing -derivedDataPath build/DerivedData
# ** TEST BUILD SUCCEEDED **

swiftlint lint --quiet
# 0 violations

• OnboardingTemplateRecommenderTests updated to pin the new boundary: Powerful is disabled below 8 GB (tested at 6 GB) and allowed-but-warned at exactly 8 GB. Other cases (12/16/32 GB, Apple Intelligence, Quick, recommendation defaults) are unchanged.

Linked issues

None.

Risk / rollout notes

• Behavior change (onboarding only). A stock 8 GB Mac now sees Powerful as available-with-a-warning instead of disabled. Apple Intelligence tiers and the Quick/Everyday recommendation logic are unchanged.
• The warning strings now read their size from DownloadableRuntimeModel.approximateSizeLabel, so they track the catalog automatically; no hardcoded sizes remain in the recommender.

Greptile Summary

This PR lowers the Powerful-tier memory disable floor from 10 GB to 8 GB (matching the new ~2.6 GB base-model GGUF vs. the old ~5 GB instruct model), and replaces hardcoded model-size strings in warning copy with a live catalog lookup via modelSizeLabel(for:).

Confidence Score: 4/5

Safe to merge; the change is narrowly scoped to onboarding display logic with no data-persistence or auth surface touched.

The threshold change and catalog-driven copy are both straightforward, and the updated tests correctly pin the new 8 GB boundary. The one residual hardcoded value ("16 GB" in the warn-path string) could drift from powerfulWarnBelowGigabytes if that constant is later adjusted, and the "local" fallback in modelSizeLabel produces awkward copy — neither is a functional regression on the current code path.

The warn-path string in OnboardingTemplateRecommender.swift line 76 still contains a literal "16 GB" that the PR description implied was removed.

Important Files Changed

Filename	Overview
Cotabby/Support/OnboardingTemplateRecommender.swift	Lowers powerfulDisableBelowGigabytes from 10 to 8, allowing 8 GB Macs to use the Powerful tier with a warning; replaces hardcoded model size strings with modelSizeLabel(for:) reading from the catalog. One hardcoded memory value ("16 GB") remains in the warn-path copy and can drift from the powerfulWarnBelowGigabytes constant.
CotabbyTests/OnboardingTemplateRecommenderTests.swift	Updates the disable-floor test probe from 8 GB to 6 GB and the warn-floor test probe from 12 GB to 8 GB, accurately pinning the new boundary decisions. All other cases unchanged.

_{Reviews (1): Last reviewed commit: "Re-tune onboarding model recommendations..." | Re-trigger Greptile}

Greptile also left 2 inline comments on this PR.

[greptile-apps]

The model size is now derived from the catalog, but the memory ceiling "16 GB" is still hardcoded in this warning string. The PR description claims "no hardcoded sizes remain in the recommender," yet this literal can drift if powerfulWarnBelowGigabytes is ever adjusted. Deriving it from the constant keeps the copy and the logic in sync.

Suggested change

	warning = "Uses a \(modelSizeLabel(for: template)) model; may run slowly with less than 16 GB of memory."
	warning = "Uses a \(modelSizeLabel(for: template)) model; may run slowly with less than \(Int(powerfulWarnBelowGigabytes)) GB of memory."

[greptile-apps]

The fallback string "local" produces grammatically awkward warning copy — e.g. "Uses a local model, which may run slowly…" — if a template's openSourceModelFilename is absent from the catalog. A phrase that completes the sentence naturally would be less confusing to users who might see this in edge cases.

Suggested change

	downloadableModel(filename: template.openSourceModelFilename)?.approximateSizeLabel ?? "local"
	downloadableModel(filename: template.openSourceModelFilename)?.approximateSizeLabel ?? "large"

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!