feat: add the-ballad-of-chalk campaign

Cloud Empress campaign for 弗莱格, a sellsword obsessed with chalk.
Ships the brief, PC sheet, state files, a starting location, and the
session 0001 log. The opening hook and hidden truth live in gm/.

campaigns/the-ballad-of-chalk/state/knowledge.md

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+# What the PC knows
+
+The PC's working picture of the world — not the world itself. Narration may draw
+on these entries and on what the PC perceives now; anything the PC has not
+learned belongs in `../gm/`.
+
+Update this file whenever a scene reveals something, confirms a suspicion, or
+overturns a belief. A mistaken belief stays here under Suspected until the PC
+learns better, even after the GM knows the truth.
+
+## Known
+
+| Fact | Learned |
+|------|---------|
+| 巨蝉在夏天苏醒，吞噬死者与白垩。 | 常识 |
+| 第 29 次远征军涌进低地，寻找失踪的云之女帝。 | 常识 |
+| 白垩能驱动纹章与法术；要用它，得先付代价。 | 常识 |
+| 低地边缘最近的水源是灰喉井。 | 走这条道的人都知道 |
+
+## Suspected
+
+| Belief | Basis |
+|--------|-------|
+| 父母从来没有真正看得起他。 | 他离开家时他们说的话 |
+| 只要精通白垩，他们就会承认他。 | 他自己的推断，未经检验 |
+| 心灵迟钝可以靠苦功弥补。 | 他不肯承认的另一半可能是错的 |
+
+## Open questions
+
+- 我到底能不能学会白垩魔法？
+- 我的父母现在在哪里？他们要我拿出什么才肯正眼看我？
+- 那个满身泥的孩子说的是真的吗？