fix(#1091): thread install scope into skill converters so local Antigravity/Copilot installs use workspace paths (#1092)

The skills layout wrapper (skillsKind) invoked every per-runtime skill
converter as realConverter(content, skillName, runtime, cmdNames). The
3rd positional arg is overloaded: claude/kimi/cline converters read
`runtime` there, but the copilot/antigravity converters read `isGlobal`
there — so they received the truthy runtime string and always took the
global path branch, leaking ~/.gemini/antigravity/ and ~/.copilot/ into
local/workspace installs instead of .agent/ and .github/.

Thread `scope` from resolveRuntimeArtifactLayout -> dispatchKindEntry ->
skillsKind, derive isGlobal = scope === 'global', and pass it as a
non-colliding 5th positional arg. Move isGlobal out of the colliding 3rd
slot in the two converter signatures (3rd/4th become ignored
_runtime/_cmdNames, matching the kimi convention). The fix flows through
the shared ArtifactKind.stage closure, so applySurface re-apply inherits
it via the same seam.

Regression test exercises the wrapper seam (installRuntimeArtifacts at
local scope) for both runtimes and asserts workspace paths, not global.

Closes #1091

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.changeset/steady-otters-leap.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 1092
+---
+**Workspace (local) Antigravity and Copilot skill installs no longer point at the global config home** — a local install rewrote `~/.claude/` references in `SKILL.md` bodies to the global `~/.gemini/antigravity/` / `~/.copilot/` paths instead of the workspace-relative `.agent/` / `.github/`, because the skills layout wrapper passed the runtime name into the converter's `isGlobal` parameter slot. (#1092)