feat: add DjVu conversion support

[al-n]

Summary

• install DjVuLibre's ddjvu utility in the production image
• add DjVu-to-PDF and DjVu-to-TIFF conversion through ddjvu
• register and document the new converter
• add unit coverage for converter metadata, command arguments, logging, and failures

Notes

ddjvu renders each page into the resulting PDF or TIFF. This supports scanned/image-only DjVu documents that Calibre cannot convert, but it does not preserve an embedded searchable text layer.

Testing

• bun test — 107 passed, 8 skipped, 0 failed
• tsc --noEmit
• knip
• Prettier and ESLint checks for the changed TypeScript files

Closes #583

---

Summary by cubic

Adds DjVu-to-PDF and DjVu-to-TIFF conversion via ddjvu, so DjVu inputs that previously failed now convert. Output is rasterized; embedded searchable text is not preserved.

• Installs djvulibre-bin.
• Registers a dedicated djvu converter for .djvu/.djv and restores its priority ahead of generic document converters.
• Runs ddjvu -format=<pdf|tiff> and logs stdout/stderr.
• Updates README and adds unit tests.

Rollout

• No API changes.
• Local development must install djvulibre-bin or use the updated image.

^{Written for commit b9f49f0. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files

_{Re-trigger cubic}

[Copilot]

Pull request overview

Adds first-class DjVu conversion support by installing DjVuLibre tooling in the production image, registering a new DjVu converter, and adding unit tests + documentation so DjVu inputs can be converted to PDF/TIFF via ddjvu.

Changes:

• Install djvulibre-bin (for ddjvu) in the Docker release image.
• Add a new djvu converter and register it in the converter dispatch table.
• Add unit tests for converter metadata/arguments and document the converter in the README.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Dockerfile	Installs djvulibre-bin to provide ddjvu in the production image.
src/converters/djvu.ts	Introduces ddjvu-based DjVu→PDF/TIFF conversion implementation.
src/converters/main.ts	Registers the new converter in the global dispatch table.
tests/converters/djvu.test.ts	Adds unit tests for DjVu converter properties and invocation args (plus common converter behaviors).
README.md	Documents DjVuLibre as a supported converter and updates counts.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[cubic-dev-ai]

All reported issues were addressed across 4 files (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P1: Moving djvu before calibre does not prioritize ddjvu, because mainConverter continues scanning and lets the later Calibre match overwrite the selected converter. Stop discovery after the first match or otherwise make the selection logic honor this priority, so DjVu-to-PDF uses ddjvu.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At src/converters/main.ts, line 85:

<comment>Moving `djvu` before `calibre` does not prioritize `ddjvu`, because `mainConverter` continues scanning and lets the later Calibre match overwrite the selected converter. Stop discovery after the first match or otherwise make the selection logic honor this priority, so DjVu-to-PDF uses `ddjvu`.</comment>

<file context>
@@ -82,6 +82,10 @@ const properties: Record<
     properties: propertiesxelatex,
     converter: convertxelatex,
   },
+  djvu: {
+    properties: propertiesDjvu,
+    converter: convertDjvu,
</file context>

✅ Addressed in b9f49f0

[al-n]

Okay, I checked this carefully, the previous version should've been the correct one - sorry, I might have misunderstood your comment @C4illin (I thought you meant that the AI review was correct but I guess you meant that the code was correct)

[C4illin]

no I meant the AI was correct but now it is wrong :)

[C4illin]

Or it is correct now again but that's a feature not a bug. You should be able to use calibre if you want