feat: implement wiki-linked categories with graph and backlinks integration

Add complete category system that integrates with Obsidian's wiki-linked
category frontmatter. Categories appear as pills on pages and link directly
to category notes (not aggregation pages).

Features:
- Parse [[Page Name]] syntax from category frontmatter
- Display category pills styled like tags
- Link directly to category notes
- Integrate with graph view connections
- Enable bidirectional backlinks
- Preserve case in category slugs

Implementation:
- Added extractWikiLinks() to frontmatter transformer
- Created CategoryList component for pill rendering
- Modified links transformer to include categories in links array
- Updated contentIndex to export category metadata
- Added i18n strings for category UI elements
- Set includeEmptyFiles: true to show empty category pages in graph

Files modified:
- quartz/plugins/transformers/frontmatter.ts
- quartz/plugins/transformers/links.ts
- quartz/plugins/emitters/contentIndex.tsx
- quartz/components/CategoryList.tsx (new)
- quartz/components/pages/CategoryContent.tsx (new)
- quartz/plugins/emitters/categoryPage.tsx (new)
- quartz/i18n/locales/en-US.ts
- quartz/i18n/locales/definition.ts
- quartz/components/index.ts
- quartz.layout.ts
- quartz.config.ts
- README.md (updated with Quartz updater documentation)

Security: Comprehensive privacy review confirms NO information leaks from
private folder. All ignore patterns working correctly.

Docs: Added CUSTOMIZATIONS.md with complete feature documentation,
implementation details, and privacy audit results.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

quartz/components/pages/CategoryContent.tsx

@@ -0,0 +1,133 @@
+import { QuartzComponent, QuartzComponentConstructor, QuartzComponentProps } from "../types"
+import style from "../styles/listPage.scss"
+import { PageList, SortFn } from "../PageList"
+import { FullSlug, getAllSegmentPrefixes, resolveRelative, simplifySlug } from "../../util/path"
+import { QuartzPluginData } from "../../plugins/vfile"
+import { Root } from "hast"
+import { htmlToJsx } from "../../util/jsx"
+import { i18n } from "../../i18n"
+import { ComponentChildren } from "preact"
+import { concatenateResources } from "../../util/resources"
+
+interface CategoryContentOptions {
+  sort?: SortFn
+  numPages: number
+}
+
+const defaultOptions: CategoryContentOptions = {
+  numPages: 10,
+}
+
+export default ((opts?: Partial<CategoryContentOptions>) => {
+  const options: CategoryContentOptions = { ...defaultOptions, ...opts }
+
+  const CategoryContent: QuartzComponent = (props: QuartzComponentProps) => {
+    const { tree, fileData, allFiles, cfg } = props
+    const slug = fileData.slug
+
+    if (!(slug?.startsWith("categories/") || slug === "categories")) {
+      throw new Error(`Component "CategoryContent" tried to render a non-category page: ${slug}`)
+    }
+
+    const category = simplifySlug(slug.slice("categories/".length) as FullSlug)
+    const allPagesWithCategory = (category: string) =>
+      allFiles.filter((file) =>
+        (file.frontmatter?.categories ?? []).flatMap(getAllSegmentPrefixes).includes(category),
+      )
+
+    const content = (
+      (tree as Root).children.length === 0
+        ? fileData.description
+        : htmlToJsx(fileData.filePath!, tree)
+    ) as ComponentChildren
+    const cssClasses: string[] = fileData.frontmatter?.cssclasses ?? []
+    const classes = cssClasses.join(" ")
+    if (category === "/") {
+      const categories = [
+        ...new Set(
+          allFiles.flatMap((data) => data.frontmatter?.categories ?? []).flatMap(getAllSegmentPrefixes),
+        ),
+      ].sort((a, b) => a.localeCompare(b))
+      const categoryItemMap: Map<string, QuartzPluginData[]> = new Map()
+      for (const category of categories) {
+        categoryItemMap.set(category, allPagesWithCategory(category))
+      }
+      return (
+        <div class="popover-hint">
+          <article class={classes}>
+            <p>{content}</p>
+          </article>
+          <p>{i18n(cfg.locale).pages.categoryContent.totalCategories({ count: categories.length })}</p>
+          <div>
+            {categories.map((category) => {
+              const pages = categoryItemMap.get(category)!
+              const listProps = {
+                ...props,
+                allFiles: pages,
+              }
+
+              const contentPage = allFiles.filter((file) => file.slug === `categories/${category}`).at(0)
+
+              const root = contentPage?.htmlAst
+              const content =
+                !root || root?.children.length === 0
+                  ? contentPage?.description
+                  : htmlToJsx(contentPage.filePath!, root)
+
+              const categoryListingPage = `/categories/${category}` as FullSlug
+              const href = resolveRelative(fileData.slug!, categoryListingPage)
+
+              return (
+                <div>
+                  <h2>
+                    <a class="internal category-link" href={href}>
+                      {category}
+                    </a>
+                  </h2>
+                  {content && <p>{content}</p>}
+                  <div class="page-listing">
+                    <p>
+                      {i18n(cfg.locale).pages.categoryContent.itemsUnderCategory({ count: pages.length })}
+                      {pages.length > options.numPages && (
+                        <>
+                          {" "}
+                          <span>
+                            {i18n(cfg.locale).pages.categoryContent.showingFirst({
+                              count: options.numPages,
+                            })}
+                          </span>
+                        </>
+                      )}
+                    </p>
+                    <PageList limit={options.numPages} {...listProps} sort={options?.sort} />
+                  </div>
+                </div>
+              )
+            })}
+          </div>
+        </div>
+      )
+    } else {
+      const pages = allPagesWithCategory(category)
+      const listProps = {
+        ...props,
+        allFiles: pages,
+      }
+
+      return (
+        <div class="popover-hint">
+          <article class={classes}>{content}</article>
+          <div class="page-listing">
+            <p>{i18n(cfg.locale).pages.categoryContent.itemsUnderCategory({ count: pages.length })}</p>
+            <div>
+              <PageList {...listProps} sort={options?.sort} />
+            </div>
+          </div>
+        </div>
+      )
+    }
+  }
+
+  CategoryContent.css = concatenateResources(style, PageList.css)
+  return CategoryContent
+}) satisfies QuartzComponentConstructor