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/SKILL.md

@@ -0,0 +1,100 @@
+---
+name: add-pdf-reader
+description: Add PDF reading to NanoClaw agents. Extracts text from PDFs via pdftotext CLI. Handles WhatsApp attachments, URLs, and local files.
+---
+
+# Add PDF Reader
+
+Adds PDF reading capability to all container agents using poppler-utils (pdftotext/pdfinfo). PDFs sent as WhatsApp attachments are auto-downloaded to the group workspace.
+
+## Phase 1: Pre-flight
+
+### Check if already applied
+
+Read `.nanoclaw/state.yaml`. If `add-pdf-reader` is in `applied_skills`, skip to Phase 3 (Verify).
+
+## Phase 2: Apply Code Changes
+
+### Initialize skills system (if needed)
+
+If `.nanoclaw/` directory doesn't exist:
+
+```bash
+npx tsx scripts/apply-skill.ts --init
+```
+
+### Apply the skill
+
+```bash
+npx tsx scripts/apply-skill.ts .claude/skills/add-pdf-reader
+```
+
+This deterministically:
+- Adds `container/skills/pdf-reader/SKILL.md` (agent-facing documentation)
+- Adds `container/skills/pdf-reader/pdf-reader` (CLI script)
+- Three-way merges `poppler-utils` + COPY into `container/Dockerfile`
+- Three-way merges PDF attachment download into `src/channels/whatsapp.ts`
+- Three-way merges PDF tests into `src/channels/whatsapp.test.ts`
+- Records application in `.nanoclaw/state.yaml`
+
+If merge conflicts occur, read the intent files:
+- `modify/container/Dockerfile.intent.md`
+- `modify/src/channels/whatsapp.ts.intent.md`
+- `modify/src/channels/whatsapp.test.ts.intent.md`
+
+### Validate
+
+```bash
+npm test
+npm run build
+```
+
+### Rebuild container
+
+```bash
+./container/build.sh
+```
+
+### Restart service
+
+```bash
+launchctl kickstart -k gui/$(id -u)/com.nanoclaw  # macOS
+# Linux: systemctl --user restart nanoclaw
+```
+
+## Phase 3: Verify
+
+### Test PDF extraction
+
+Send a PDF file in any registered WhatsApp chat. The agent should:
+1. Download the PDF to `attachments/`
+2. Respond acknowledging the PDF
+3. Be able to extract text when asked
+
+### Test URL fetching
+
+Ask the agent to read a PDF from a URL. It should use `pdf-reader fetch <url>`.
+
+### Check logs if needed
+
+```bash
+tail -f logs/nanoclaw.log | grep -i pdf
+```
+
+Look for:
+- `Downloaded PDF attachment` — successful download
+- `Failed to download PDF attachment` — media download issue
+
+## Troubleshooting
+
+### Agent says pdf-reader command not found
+
+Container needs rebuilding. Run `./container/build.sh` and restart the service.
+
+### PDF text extraction is empty
+
+The PDF may be scanned (image-based). pdftotext only handles text-based PDFs. Consider using the agent-browser to open the PDF visually instead.
+
+### WhatsApp PDF not detected
+
+Verify the message has `documentMessage` with `mimetype: application/pdf`. Some file-sharing apps send PDFs as generic files without the correct mimetype.