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/ch7-open-book.md

@@ -0,0 +1,28 @@
+---
+title: "Open Book — Python Source"
+event: "GEMASTIK 2026 Warmup"
+challenge: "Open Book"
+category: "misc"
+points: 500
+difficulty: "easy"
+flag: "GEMASTIK19{pyth0n_s0urc3_t3rbuka}"
+---
+
+# Open Book (500 pts) — Misc / Source
+
+**File:** `chall.py`
+
+Password yang benar **langsung dicetak dari array `SECRET`** (ASCII codes):
+
+```python
+SECRET = [71, 69, 77, 65, 83, 84, 73, 75, 49, 57, 123, 112, 121, 116, 104, 48, 110, 95,
+          115, 48, 117, 114, 99, 51, 95, 116, 51, 114, 98, 117, 107, 97, 125]
+
+flag = "".join(chr(c) for c in SECRET)
+print(flag)
+# GEMASTIK19{pyth0n_s0urc3_t3rbuka}
+```
+
+## Flag
+
+`GEMASTIK19{pyth0n_s0urc3_t3rbuka}`