fix(#1615): normalize Windows backslash paths in workflow content

computePathPrefix returned a Windows-style path (with backslashes from path.join) into markdown @-references. Workflow file content on Windows ended up with mixed separators, breaking substring checks in install/install-runtime-artifacts tests on windows-latest CI only.

Normalize resolvedTarget and homeDir to forward slashes inside computePathPrefix. The prefix is always substituted into markdown body text, which uses POSIX paths universally. Idempotent on POSIX.

Also normalizes the two test assertions to forward-slash form so they pass on Windows. Adds a regression test for backslash-style input.

Documents DEFECT.WINDOWS-PATH-LEAK-IN-MARKDOWN-CONTENT + RULESET.CONTENT-PATH-NORMALIZATION in CONTEXT.md so this anti-pattern stops recurring.

tests/install-runtime-artifacts.test.cjs

@@ -315,7 +315,7 @@ describe('installRuntimeArtifacts — windsurf workflows layout (#1615)', () =>
     const helpContent = fs.readFileSync(path.join(workflowsDir, 'gsd-help.md'), 'utf8');
     assert.ok(!helpContent.startsWith('---'), 'Windsurf workflows must be plain markdown, not SKILL.md frontmatter');
     assert.match(helpContent, /# gsd-help/, 'workflow should identify the slash command it backs');
-    assert.ok(helpContent.includes(`${configDir}/gsd-core/commands/gsd/help.md`),
+    assert.ok(helpContent.includes(`${configDir}/gsd-core/commands/gsd/help.md`.replace(/\\/g, '/')),
       'workflow should reference the installed command body using the actual install target');
 
     for (const fileName of fs.readdirSync(workflowsDir)) {