Submit the two verified Skip upstream PRs (Gradient.Stop init, MeshGradient)

[rozd]

Two upstream changes were implemented on local skiptools forks and verified against a five-point bar, but no PR has been opened. Both unblock follow-up work here (#20, #21).

1. Gradient.Stop public init (skip-fuse-ui) — one-line parity fix. Verified with a positive build, a negative control, and a device log.

2. MeshGradient via an AGSL ShaderBrush (skip-ui → skip-fuse-ui → showcase) — verified on emulators at API 36 and API 32, with a negative control and a ThemeKit build against the fork. One gap remains: the showcase app-harness run, deferred over a skip CLI 1.9.5 vs showcase-HEAD Gradle skew. That needs closing before submission.

Before opening anything:

• sign Skip's Contributor Agreement — a per-account one-off, worth doing ahead of time rather than discovering it with PRs ready
• Skip's PR template requires swift test (not skip test) to have been run locally and has a mandatory AI-disclosure section
• respect the paired-PR convention in skip-fuse-ui's ADDING_MODIFIERS.md: skip-ui → skip-fuse-ui → skipapp-showcase-fuse, cross-linked
• cheapest reviewer cost first: the Gradient.Stop fix, then mesh
• never reference fork URLs from anything ThemeKit publishes — SKIP_DEPENDENCY_ROOT stays the only path

Draft PR bodies and the evidence logs are in the local planning notes (tmp/mesh-pr-drafts.md, tmp/phase2-evidence.md), which are untracked.