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.

dev-docs/frontend.md

@@ -53,7 +53,7 @@ Two independent things have to be true, and both were violated at some point:
 | `sidebar.js` | `<app-sidebar>` | Nav sidebar; role-driven (`ui_mode`); inbox badge is **live** — the chat WS forwards the inbox lifecycle events (`approval_requested/resolved`, `clarification_*`, `elicitation_*`) regardless of `source`, `chat-session.js` re-dispatches them as the `inbox-changed` window event, and the sidebar (+ `agent-inbox.js`) refreshes on it; a 60 s poll remains as fallback |
 | `topbar.js` | `<app-topbar>` | Top nav bar; per-user avatar color hashed from the username |
 | `dashboard-page.js` | `<dashboard-page>` | `#dashboard` — status hero, LLM stats charts, pending inbox, quick guide |
-| `shared/file-viewer-base.js` | `FileViewerBase` (base) | Shared file-viewer engine (fetch, kind detection, markdown/PDF/SVG/LaTeX, watcher, `_renderBody`); driven by `_show`/`_hide`. Extended by desktop + mobile |
+| `shared/file-viewer-base.js` | `FileViewerBase` (base) | Shared file-viewer engine (fetch, kind detection, markdown/PDF/SVG/LaTeX/word-docs, watcher, `_renderBody`); driven by `_show`/`_hide`. Extended by desktop + mobile |
 | `file-viewer-page.js` | `<file-viewer-page>` | Desktop file viewer: `FileViewerBase` + hash routing via `window.openFile(path)` → `#file_viewer?path=...` |
 | `shared/file-viewer-mobile.js` | `<mobile-file-viewer-page>` | Mobile file viewer: `FileViewerBase` + prop-driven (`visible`/`path`), full-screen with back button |
 | `agents.js` | `<agents-page>` | Agent discovery and config |
@@ -81,3 +81,11 @@ Two independent things have to be true, and both were violated at some point:
 | `models-tts.js` | `<models-tts-section>` | Text-to-speech model CRUD |
 | `mobile-app.js` | `<mobile-app>` | Mobile app shell |
 | `shared/settings-page.js` | `<settings-page>` | Mobile settings: per-user avatar, locale picker (`I18nMixin`), profile/preferences |
+
+## Server-rendered kinds in the file viewer (LaTeX, word documents)
+
+Two kinds are not served as-is but rendered to PDF server-side on demand: `.tex`/`.latex` (kind `latex`, `?compile-latex=true`, `latexmk`) and `.docx`/`.doc`/`.odt`/`.rtf` (kind `docx`, `?compile-docx=true`, LibreOffice — `skald_core::docx::DocxConverter`, content-hash cache, no dependency graph). Both render through the same `<pdf-view>` and degrade gracefully when the host tool is missing (`501`) or the run fails (`422`): the viewer fetches the flagged URL, keeps the error body, and falls back. Three asymmetries between the two, each deliberate:
+
+- **Fallback content.** A failed LaTeX compile still shows the *source* (readable); a word document is a zip, so its fallback is the binary download state with the reason in a foldable block on top — there is no source to show.
+- **Download.** A `.tex` downloads the *compiled PDF* (the source is useless to most people); a word document downloads the **original file** — it is itself the editable artifact someone asking "send me the document" wants, and the PDF is only the preview mechanism.
+- **Watching.** A `.tex` subscription expands server-side to its `.fls` dependency set (`file_watch.rs`); a word document is self-contained, so the plain per-file watcher already covers it and a change re-converts via the content-keyed cache — `file_watch.rs` needed no branch. Container-only word documents still convert (the API shuttles the bytes out, see `filesystem-and-containers.md`) but, like any container-only path, they are not watchable.