feat(skills): add pdf-reader skill (#772)

Thanks @glifocat! Clean skill package — good docs, solid tests, nice intent files. Pushed a small fix for path traversal on the PDF filename before merging.

.claude/skills/add-pdf-reader/modify/container/Dockerfile.intent.md

@@ -0,0 +1,23 @@
+# Intent: container/Dockerfile modifications
+
+## What changed
+Added PDF reading capability via poppler-utils and a custom pdf-reader CLI script.
+
+## Key sections
+
+### apt-get install (system dependencies block)
+- Added: `poppler-utils` to the package list (provides pdftotext, pdfinfo, pdftohtml)
+- Changed: Comment updated to mention PDF tools
+
+### After npm global installs
+- Added: `COPY skills/pdf-reader/pdf-reader /usr/local/bin/pdf-reader` to copy CLI script
+- Added: `RUN chmod +x /usr/local/bin/pdf-reader` to make it executable
+
+## Invariants (must-keep)
+- All Chromium dependencies unchanged
+- agent-browser and claude-code npm global installs unchanged
+- WORKDIR, COPY agent-runner, npm install, npm run build sequence unchanged
+- Workspace directory creation unchanged
+- Entrypoint script unchanged
+- User switching (node user) unchanged
+- ENTRYPOINT unchanged