fix: decouple Head.tsx from og-image plugin import (#2495)

Remove unconditional import of CustomOgImagesEmitterName from
.quartz/plugins in Head.tsx. This caused builds to fail when the
og-image plugin was not listed in quartz.config.yaml, violating the
plugin system's opt-in contract.

The fix inlines the emitter name string constant at the usage site.

Also convert the ContentDetails import in fileTrie.ts to
`import type` since it is only used in a type position.

quartz/components/Head.tsx

@@ -4,7 +4,7 @@ import { CSSResourceToStyleElement, JSResourceToScriptElement } from "../util/re
 import { googleFontHref, googleFontSubsetHref } from "../util/theme"
 import { QuartzComponent, QuartzComponentConstructor, QuartzComponentProps } from "./types"
 import { unescapeHTML } from "../util/escape"
-import { CustomOgImagesEmitterName } from "../../.quartz/plugins"
+
 export default (() => {
   const Head: QuartzComponent = ({
     cfg,
@@ -31,9 +31,7 @@ export default (() => {
     const socialUrl =
       fileData.slug === "404" ? url.toString() : joinSegments(url.toString(), fileData.slug!)
 
-    const usesCustomOgImage = ctx.cfg.plugins.emitters.some(
-      (e) => e.name === CustomOgImagesEmitterName,
-    )
+    const usesCustomOgImage = ctx.cfg.plugins.emitters.some((e) => e.name === "CustomOgImages")
     const ogImageDefaultPath = `https://${cfg.baseUrl}/static/og-image.png`
 
     const coreStylesheet = css[0]?.content