feat: add personal skills settings UI and docs (#25066)

> Mux updated this PR on behalf of Mike.

## Summary

- Add experimental personal skills API helpers and an Agents settings UI
for listing, creating, editing, deleting, and importing SKILL.md
content.
- Add docs, Storybook coverage, and unit tests for backend-compatible
SKILL.md parsing.
- Address review feedback by simplifying frontmatter scalar parsing,
clarifying the UI parser scope, defaulting personal skill queries to
`me`, and patching React Query caches after create, update, and delete.
- Merge latest `main` and resolve the Agents sidebar refactor conflicts.

## Validation

- pre-commit hook
- `go test ./codersdk/workspacesdk -run TestParseSkillFrontmatter
-count=1`
- `go test ./coderd/x/chatd/chattool -run 'Test' -count=1`
- `cd site && pnpm test --
src/pages/AgentsPage/utils/personalSkills.test.ts
src/api/queries/userSkills.test.ts src/utils/fileSize.test.ts
--runInBand`
- `cd site && pnpm lint:types`
- `cd site && pnpm lint:check`

codersdk/workspacesdk/frontmatter.go

@@ -24,6 +24,29 @@ var markdownCommentRe = regexp.MustCompile(`<!--[\s\S]*?-->`)
 // the frontmatter is missing a required name field.
 var ErrFrontmatterNameRequired = xerrors.New("frontmatter missing required 'name' field")
 
+func unquoteFrontmatterScalar(value string) string {
+	if len(value) < 2 {
+		return value
+	}
+
+	quote := value[0]
+	if quote != value[len(value)-1] {
+		return value
+	}
+
+	inner := value[1 : len(value)-1]
+	switch quote {
+	case '"':
+		// This parser supports a small SKILL.md scalar subset, not full
+		// YAML. Double quotes only unescape quoted text and Windows paths.
+		return strings.NewReplacer(`\"`, `"`, `\\`, `\`).Replace(inner)
+	case '\'':
+		return inner
+	default:
+		return value
+	}
+}
+
 // ParseSkillFrontmatter extracts name, description, and the
 // remaining body from a skill meta file. The expected format is
 // YAML-ish frontmatter delimited by "---" lines:
@@ -62,13 +85,7 @@ func ParseSkillFrontmatter(content string) (name, description, body string, err
 		}
 		key = strings.TrimSpace(key)
 		value = strings.TrimSpace(value)
-		// Strip surrounding quotes from YAML string values.
-		if len(value) >= 2 {
-			if (value[0] == '"' && value[len(value)-1] == '"') ||
-				(value[0] == '\'' && value[len(value)-1] == '\'') {
-				value = value[1 : len(value)-1]
-			}
-		}
+		value = unquoteFrontmatterScalar(value)
 		switch strings.ToLower(key) {
 		case "name":
 			name = value

codersdk/workspacesdk/frontmatter_test.go

@@ -32,6 +32,24 @@ func TestParseSkillFrontmatter(t *testing.T) {
 		require.Equal(t, "single-quoted", desc)
 	})
 
+	t.Run("EscapedDoubleQuotedValue", func(t *testing.T) {
+		t.Parallel()
+		_, desc, _, err := workspacesdk.ParseSkillFrontmatter(
+			"---\nname: escaped\ndescription: \"Review \\\"critical\\\" C:\\\\paths.\"\n---\nBody\n",
+		)
+		require.NoError(t, err)
+		require.Equal(t, "Review \"critical\" C:\\paths.", desc)
+	})
+
+	t.Run("PlainHashValue", func(t *testing.T) {
+		t.Parallel()
+		_, desc, _, err := workspacesdk.ParseSkillFrontmatter(
+			"---\nname: plain-hash\ndescription: Build # test\n---\nBody\n",
+		)
+		require.NoError(t, err)
+		require.Equal(t, "Build # test", desc)
+	})
+
 	t.Run("NoDescription", func(t *testing.T) {
 		t.Parallel()
 		name, desc, body, err := workspacesdk.ParseSkillFrontmatter(