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/ch2-julius.md

@@ -0,0 +1,29 @@
+---
+title: "Julius — ROT13 Caesar Cipher"
+event: "GEMASTIK 2026 Warmup"
+challenge: "Julius"
+category: "crypto"
+points: 500
+difficulty: "easy"
+flag: "GEMASTIK19{caesar_r0t_th1rt33n_klasik}"
+---
+
+# Julius (500 pts) — Caesar / ROT13
+
+**File:** `chall.txt` → `TRZNFGVX19{pnrfne_e0g_gu1eg33a_xynfvx}`
+
+Caesar cipher dengan pergeseran paling populer di internet = **ROT13** (geser 13).
+`TRZNFGVX19` → `GEMASTIK19`, dst.
+
+```python
+import codecs
+
+s = "TRZNFGVX19{pnrfne_e0g_gu1eg33a_xynfvx}"
+flag = codecs.encode(s, "rot_13")
+print(f"Flag: {flag}")
+# Output: GEMASTIK19{caesar_r0t_th1rt33n_klasik}
+```
+
+## Flag
+
+`GEMASTIK19{caesar_r0t_th1rt33n_klasik}`