feat: --competitors flag for auto-discovered comparison fan-out (#308)

Pass `--competitors` on a single-entity topic and the engine auto-discovers
2-6 peer entities via web search, runs the full pipeline on each in
parallel, and returns one N-way comparison reusing the existing 9-axis
Head-to-Head scaffold. `last30days OpenAI --competitors` resolves to
Anthropic + xAI + Google Gemini; `last30days Kanye West --competitors`
resolves to Drake + Kendrick Lamar + one more peer.

- New CLI flags: --competitors, --competitors=N, --competitors-list
- New scripts/lib/competitors.py — mirrors resolve.auto_resolve pattern
  (web search + deterministic text extraction, no internal LLM)
- New scripts/lib/fanout.py — ThreadPoolExecutor orchestrator; per-entity
  failures degrade gracefully as long as >=2 entities survive
- Multi-report render in scripts/lib/render.py reuses the comparison
  scaffold for the synthesis table
- LAW 7-style stderr when no backend and no list, pointing the hosting
  reasoning model at --competitors-list
- 38 new tests across CLI parsing, discovery, fanout, and rendering

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "last30days",
-  "version": "3.0.10",
+  "version": "3.0.11",
   "description": "Research any topic across Reddit, X, YouTube, TikTok, Instagram, Hacker News, Polymarket, GitHub, and 5+ more sources. AI agent scores by upvotes, likes, and real money - not editors.",
   "author": {
     "name": "Matt Van Horn",