feat: base64 import - #2469

This PR addresses issue #2458 by adding support for importing embedded Base64 (data URI) assets in standalone HTML/Markdown page imports, materializing them as stored attachments so the imported content can reference /api/files/... paths.

Changes:

• Wrap standalone page import creation in a DB transaction and generate a page ID upfront for attachment linking.
• Add processEmbeddedAttachments() to detect Base64 data: URIs in HTML and upload them as attachments, rewriting src/href.
• Add MIME-type → extension resolution and enforce upload size limits for embedded payloads.

Suppressed comments (4)

apps/server/src/integrations/import/services/import-attachment.service.ts:116

• href can be undefined, so calling trim() can throw at runtime. This loop should follow the same safe normalization/caching logic as the src loop (including treating “not processed yet” differently from a cached null result).

      const $element = $(element);
      const href = $element.attr('href');
      const normalized = href.trim();

      let apiFilePath = processed.get(normalized);

apps/server/src/integrations/import/services/import.service.ts:149

• The outer catch block wraps all errors as "Failed to create imported page", which hides more specific BadRequestExceptions thrown inside the transaction (e.g., unsupported file types or ProseMirror conversion failures). Re-throw BadRequestException as-is and only wrap unexpected errors.

    } catch (err) {
      const message = 'Failed to create imported page';
      this.logger.error(message, err);
      throw new BadRequestException(message);
    }

apps/server/src/integrations/import/services/import.service.ts:121

• Inside the transaction, getNewPagePosition() queries via this.db (outside the passed trx), so the “read last position + insert” sequence is not atomic even though the page insert uses the transaction. Consider updating getNewPagePosition to accept an optional transaction and use dbOrTx(this.db, trx) (or inline the query here) to avoid inconsistent positions under concurrency.

        const pageTitle = title || fileName;
        const pagePosition = await this.getNewPagePosition(spaceId);

apps/server/src/integrations/import/services/import.service.ts:75

• executeTx() starts the DB transaction before running potentially expensive, non-DB work (markdown->HTML conversion, Cheerio normalization, ProseMirror/Ydoc generation). This keeps a transaction/connection open longer than necessary and can reduce throughput under load. Consider doing the pure transformation steps outside the transaction and only wrapping the DB writes (attachment rows + page insert) in executeTx.

    try {
      createdPage = await executeTx(this.db, async (trx) => {

        if (fileExtension.endsWith('.md') || fileExtension.endsWith('.html')) {
          const rawHtml = fileExtension.endsWith('.md')

• Files reviewed: 2/2 changed files
• Comments generated: 3
• Review effort level: Lite