docs: replace dummy docs with GEMASTIK 2026 Warmup writeups (ch1-14)

- Deleted all previous dummy docs (defcon-quals-2024, infra/cloudflare-525, debugging/websocket-timeout, template, docs/*, notes/*, research/*)
- Added 14 Gemastik warmup writeups covering encoding, stego, web, pwn, crypto
- ch13: RSA small factors; ch14: RSA special integers via paper-search (GCD with paper appendix primes)
- All flags recovered and documented with solution methods

content/writeups/gemastik-2026-warmup/ch5-nothing-here.md

@@ -0,0 +1,29 @@
+---
+title: "Nothing Here — Web Comment"
+event: "GEMASTIK 2026 Warmup"
+challenge: "Nothing Here"
+category: "web"
+points: 500
+difficulty: "easy"
+flag: "GEMASTIK19{v13w_s0urc3_pahlawan}"
+---
+
+# Nothing Here (500 pts) — Web
+
+**URL:** `http://15.232.89.109:8001/`
+
+Halaman bilang "tidak ada apa-apa" tapi flag ada di **HTML comment**:
+
+```html
+<!-- Catatan dev: jangan lupa hapus flag ini sebelum rilis: GEMASTIK19{v13w_s0urc3_pahlawan} -->
+```
+
+## Recon
+
+```bash
+curl -s http://15.232.89.109:8001/ | grep -i 'GEMASTIK\|<!--'
+```
+
+## Flag
+
+`GEMASTIK19{v13w_s0urc3_pahlawan}`