refactor(completions): centralize content scanning

Add a browser-safe ContentRegistry owning path and inline content
stores, then derive completions from it. Remove the old block-processor,
directive-scanner, and link-source modules in favor of scanDoc,
deriveCompletions, and injectSparkDirectives, and register an inline
resolver for the frontend file index.

src/data-loader/file-index.ts

@@ -24,6 +24,20 @@ let fileIndex: FileIndex | null = null;
 let indexLoadPromise: Promise<void> | null = null;
 let activeSource: "cli" | "folder" | null = null;
 
+/**
+ * Optional registry for resolving inline content ids (set by the journal
+ * completions module). When present, `getIndexedData` resolves ids that
+ * aren't real files through it.
+ */
+let inlineResolver: ((path: string) => string | null) | null = null;
+
+/** Register a resolver for inline content ids (see journal/completions). */
+export function setInlineResolver(
+  fn: ((path: string) => string | null) | null,
+): void {
+  inlineResolver = fn;
+}
+
 /** Currently active directory handle (if folder source) */
 let activeDirHandle: FileSystemDirectoryHandle | null = null;
 
@@ -181,6 +195,15 @@ export async function getIndexedData(path: string): Promise<string> {
   if (fileIndex && fileIndex[path]) {
     return fileIndex[path];
   }
+  // Resolve inline content ids through the registry before fetching.
+  if (inlineResolver) {
+    const inline = inlineResolver(path);
+    if (inline !== null) {
+      fileIndex = fileIndex || {};
+      fileIndex[path] = inline;
+      return inline;
+    }
+  }
   const res = await fetch(path);
   const content = await res.text();
   fileIndex = fileIndex || {};