feat(viewer): preview word documents (.docx/.doc/.odt/.rtf) as PDF

The file viewer converts word-processor documents to PDF server-side via
LibreOffice (skald_core::docx::DocxConverter), mirroring the LaTeX pipeline
but content-hash cached: the format is self-contained, so there is no
dependency graph and the file watcher needs no expansion. Container-only
documents are shuttled out and converted on the host. With no LibreOffice
installed the viewer says so and falls back to download-only. Downloads
still save the original document, not the preview PDF.

web/components/shared/file-viewer-base.js

@@ -10,8 +10,9 @@ import './pdf-view.js';   // registers <pdf-view>; pdf.js itself is imported laz
 
 /**
  * Shared file-viewer engine. Holds all of the fetch / kind-detection /
- * markdown-asset-rewriting / LaTeX-compile / live-watch logic plus `_renderBody`,
- * driven purely by two methods: `_show(path)` and `_hide()`. It carries no
+ * markdown-asset-rewriting / LaTeX-compile / word-doc-convert / live-watch
+ * logic plus `_renderBody`, driven purely by two methods: `_show(path)` and
+ * `_hide()`. It carries no
  * navigation or page chrome of its own — subclasses (desktop `<file-viewer-page>`
  * and mobile `<mobile-file-viewer-page>`) wire visibility/path to those methods
  * and provide their own `render()` header.
@@ -19,6 +20,10 @@ import './pdf-view.js';   // registers <pdf-view>; pdf.js itself is imported laz
 
 const IMG_EXTS  = ['png', 'jpg', 'jpeg', 'gif', 'webp', 'bmp', 'ico', 'avif'];
 const LATEX_EXTS = ['tex', 'latex'];
+// Word-processor documents, converted to PDF server-side via LibreOffice
+// (`?compile-docx=true`). Unlike LaTeX there is no readable source to fall
+// back to: a failed or unavailable conversion leaves the binary state.
+const WORD_EXTS  = ['docx', 'doc', 'odt', 'rtf'];
 const TEXT_EXTS = [
   'txt', 'md', 'markdown', 'rs', 'js', 'mjs', 'cjs', 'ts', 'tsx', 'jsx',
   'py', 'json', 'yml', 'yaml', 'toml', 'sh', 'bash', 'zsh', 'fish',
@@ -54,6 +59,7 @@ export function kindFor(path) {
   // (srcdoc + sandbox="allow-scripts", no allow-same-origin) — see _renderBody.
   if (ext === 'html' || ext === 'htm') return 'html';
   if (LATEX_EXTS.includes(ext))  return 'latex';
+  if (WORD_EXTS.includes(ext))   return 'docx';
   if (TEXT_EXTS.includes(ext))   return 'text';
   return 'binary';
 }
@@ -137,6 +143,7 @@ const VIEW_KINDS = {
   svg:    'an SVG image',
   html:   'a rendered HTML page',
   latex:  'a compiled LaTeX document',
+  docx:   'an office document converted to PDF',
   binary: 'a binary file, whose content is not displayed',
 };
 
@@ -391,7 +398,10 @@ export class FileViewerBase extends LightElement {
 
   /**
    * Download the current file. LaTeX sources always download the compiled PDF
-   * (`compile-latex=true`); every kind is served with `force_download=true` so
+   * (`compile-latex=true`); word documents instead download the **original**
+   * file — unlike a `.tex` source, a `.docx` is itself the editable document
+   * people want to keep or send, while the PDF is only the preview mechanism.
+   * Every kind is served with `force_download=true` so
    * the server sets `Content-Disposition: attachment` and the browser saves it
    * (with the server-supplied name) instead of rendering inline.
    */
@@ -488,6 +498,8 @@ export class FileViewerBase extends LightElement {
         if (oldUrl) URL.revokeObjectURL(oldUrl);
       } else if (this._kind === 'latex') {
         await this._loadLatex(path);
+      } else if (this._kind === 'docx') {
+        await this._loadDocx(path);
       } else if (this._kind === 'text' || this._kind === 'html') {
         const res = await fetch(url);
         if (!res.ok) throw new Error(`HTTP ${res.status}`);
@@ -551,6 +563,39 @@ export class FileViewerBase extends LightElement {
     this._content = await res.text();
   }
 
+  /**
+   * Load a word-processor document (`.docx` / `.doc` / `.odt` / `.rtf`).
+   * Asks the server to convert it to PDF via LibreOffice; on any non-OK
+   * response (501 no LibreOffice, 504 timeout, 422 conversion error) there is
+   * no readable source to fall back to — the body is a zip — so the reason is
+   * kept in `_compileError` and `_renderBody` shows the binary state with the
+   * error block on top.
+   */
+  async _loadDocx(path) {
+    const convertUrl = this._fileUrl(path, { 'compile-docx': 'true' });
+    try {
+      const res = await fetch(convertUrl);
+      if (res.ok) {
+        const blob = await res.blob();
+        // Swap URLs only after the new blob is ready so the preview never flickers.
+        const oldUrl = this._blobUrl;
+        this._blobUrl = URL.createObjectURL(blob);
+        if (oldUrl) URL.revokeObjectURL(oldUrl);
+        this._compileError = null;
+        return;
+      }
+      // The error body is a short plain-text reason (converter missing,
+      // timeout, or the captured soffice output) — shown verbatim, unlike the
+      // latex log which needs distilling.
+      let detail = '';
+      try { detail = (await res.text()).trim(); } catch { /* ignore */ }
+      this._compileError = detail || `HTTP ${res.status}`;
+    } catch (e) {
+      this._compileError = e.message || String(e);
+    }
+    this._revokeBlobUrl();
+  }
+
   // ── History mode (git-versioned files) ─────────────────────────────────────
 
   /**
@@ -901,6 +946,10 @@ export class FileViewerBase extends LightElement {
       // a native .pdf is rendered (see the note above).
       return html`<pdf-view class="fv-pdf" .src=${this._blobUrl}></pdf-view>`;
     }
+    if (this._kind === 'docx' && this._blobUrl) {
+      // Successfully converted server-side (LibreOffice) — same render path.
+      return html`<pdf-view class="fv-pdf" .src=${this._blobUrl}></pdf-view>`;
+    }
     if (this._kind === 'svg' && this._blobUrl) {
       // `allow-same-origin` (and nothing else) is required so the iframe can load
       // the blob: URL — those are only readable from their creating origin. With
@@ -910,6 +959,23 @@ export class FileViewerBase extends LightElement {
         ${keyed(this._blobUrl, html`<iframe class="fv-svg" sandbox="allow-same-origin" src=${this._blobUrl} title=${this._path}></iframe>`)}
       </div>`;
     }
+    if (this._kind === 'docx') {
+      // Conversion failed or LibreOffice is not installed — unlike LaTeX
+      // there is no readable source to show (the file is a zip), so the
+      // reason sits in a foldable block over the download-only state.
+      return html`
+        ${this._compileError
+          ? html`<details class="fv-compile-error">
+              <summary><i class="bi bi-exclamation-triangle text-warning"></i>&nbsp;${t('fv.docx_failed')}</summary>
+              <pre>${this._compileError}</pre>
+            </details>`
+          : nothing}
+        <div class="fv-state text-muted">
+          <i class="bi bi-file-earmark-word fs-3 d-block mb-2"></i>
+          ${t('fv.binary_unavailable')}
+        </div>
+      `;
+    }
     if (this._kind === 'binary') {
       return html`<div class="fv-state text-muted">
         <i class="bi bi-file-earmark-binary fs-3 d-block mb-2"></i>