Replace Pi tool registrations with skills and CLI integration

- Remove all manually registered Pi tools (alpha_search, alpha_get_paper,
  alpha_ask_paper, alpha_annotate_paper, alpha_list_annotations,
  alpha_read_code, session_search, preview_file) and their wrappers
  (alpha.ts, preview.ts, session-search.ts, alpha-tools.test.ts)
- Add Pi skill files for alpha-research, session-search, preview,
  modal-compute, and runpod-compute in skills/
- Sync skills to ~/.feynman/agent/skills/ on startup via syncBundledAssets
- Add node_modules/.bin to Pi subprocess PATH so alpha CLI is accessible
- Add /outputs extension command to browse research artifacts via dialog
- Add Modal and RunPod as execution environments in /replicate and
  /autoresearch prompts
- Remove redundant /alpha-login /alpha-logout /alpha-status REPL commands
  (feynman alpha CLI still works)
- Update README, researcher agent, metadata, and website docs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/preview/SKILL.md

@@ -0,0 +1,27 @@
+---
+name: preview
+description: Preview Markdown, LaTeX, PDF, or code artifacts in the browser or as PDF. Use when the user wants to review a written artifact, export a report, or view a rendered document.
+---
+
+# Preview
+
+Use the `/preview` command to render and open artifacts.
+
+## Commands
+
+| Command | Description |
+|---------|-------------|
+| `/preview` | Preview the most recent artifact in the browser |
+| `/preview --file <path>` | Preview a specific file |
+| `/preview-browser` | Force browser preview |
+| `/preview-pdf` | Export to PDF via pandoc + LaTeX |
+| `/preview-clear-cache` | Clear rendered preview cache |
+
+## Fallback
+
+If the preview commands are not available, use bash:
+
+```bash
+open <file.md>          # macOS — opens in default app
+open <file.pdf>         # macOS — opens in Preview
+```