enhancement(#782): emit gsd skills to ~/.cline/skills for Cline >= v3.48 (#809)

Cline added a global skills system (~/.cline/skills/<name>/SKILL.md) in
v3.48.0, but gsd treated Cline as rules-only and emitted zero skills
(getGlobalSkillsBase('cline')=null, empty artifact kinds). This makes gsd
emit skills for Cline at global scope, alongside the existing .clinerules.

- runtime-homes: getGlobalSkillsBase('cline') -> ~/.cline/skills (was null)
- runtime-artifact-layout: cline emits a skills kind for GLOBAL scope only
  (local stays .clinerules-only), mirroring claude's scope dispatch
- install.js: convertClaudeCommandToClineSkill emits name+description-only
  SKILL.md frontmatter (Cline/agentskills.io spec; no Claude-specific
  allowed-tools/argument-hint/agent), hyphen-normalized + .cline/-rewritten
  body; global cline routed through the skills path while .clinerules is
  still written; _applyRuntimeRewrites cline case handles custom
  CLINE_CONFIG_DIR; convertClaudeToCliineMarkdown also rewrites bare
  ~/.claude and CLAUDE_CONFIG_DIR
- docs: install-on-your-runtime.md documents Cline global skills vs local rules
- tests: converter (name+description-only), global emission, skills+.clinerules
  coexistence, scope-aware layout, custom-dir paths, idempotency

Closes #782

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/how-to/install-on-your-runtime.md

@@ -205,13 +205,13 @@ WINDSURF_CONFIG_DIR=~/.codeium/windsurf-alt npx @opengsd/gsd-core@latest --winds
 
 ### Cline
 
-Cline uses a rules-based integration — GSD installs as Cline rules rather than slash commands.
+GSD gives Cline both skills (≥ v3.48.0) and the `.clinerules/` directory integration — no custom slash commands are registered.
 
 ```bash
-# Global install (all projects)
+# Global install (all projects — skills + rules directory)
 npx @opengsd/gsd-core@latest --cline --global
 
-# Local install (this project only)
+# Local install (this project only — rules directory only)
 npx @opengsd/gsd-core@latest --cline --local
 ```
 
@@ -225,10 +225,16 @@ GSD writes the [`.clinerules/` directory form](https://docs.cline.bot/customizat
   GSD hook guards `.planning/` artifacts from direct edits and otherwise allows the operation;
   it fails open, so a hook error never blocks you. Cline runs hooks on macOS and Linux only.
 
-Global installs additionally merge GSD instructions into **`~/.agents/AGENTS.md`**, the
-cross-tool global instruction file Cline reads. The block is marker-delimited, so your own
-`AGENTS.md` content (and other tools' entries) is preserved, and `--uninstall` strips only the
-GSD block.
+**Global install additionally:**
+
+- Emits each GSD command as **`~/.cline/skills/<name>/SKILL.md`**. Cline ≥ v3.48.0 loads
+  skills from `~/.cline/skills/` automatically — no configuration needed.
+- Merges GSD instructions into **`~/.agents/AGENTS.md`**, the cross-tool global instruction
+  file Cline reads. The block is marker-delimited, so your own `AGENTS.md` content (and other
+  tools' entries) is preserved, and `--uninstall` strips only the GSD block.
+
+**Local install** writes the `.clinerules/` directory into the current project only. No skills
+directory is created for local scope.
 
 > Cline's *global* hook directory (`~/Documents/Cline/Rules/Hooks/`) is not yet populated by the
 > installer — project-scope hooks (`.clinerules/hooks/`) and the global `AGENTS.md` instruction