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/world/locations/README.md

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+# Locations
+
+One file per location, named `kebab-case.md`. Keep the frontmatter stable so
+the agent can update it in place.
+
+These files are player-facing: record what the PC has observed or could observe.
+A hidden truth the PC has not yet learned belongs in `../../gm/`.
+
+```markdown
+---
+name: 
+type: 
+region: 
+status: visited | known | rumored
+---
+
+# <name>
+
+## Description
+
+## Notable features
+
+## Inhabitants
+
+## History
+```

campaigns/the-ballad-of-chalk/world/locations/ash-throat-well.md

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+---
+name: 灰喉井
+type: 水站 / 驿站
+region: 低地边缘，盐碱荒原
+status: known
+---
+
+# 灰喉井
+
+## Description
+
+盐脊道上唯一还出水的井。井水发苦，烧开后有白霜浮在表面，据说那就是被冲淡的白垩。
+几间土坯房挤在井边，一面褪色的远征军旗子钉在最高的那间屋顶上，风一吹就哗啦响。
+
+## Notable features
+
+- 一口深井，水苦，但方圆几十里内没有第二处水源。
+- 来往的悬赏猎人、驮鸽商队和云裔的信使在此歇脚。
+- 墙上钉满悬赏令，很多已经褪成空白。
+
+## Inhabitants
+
+守井的老两口，姓什么没人记得。还有几只不肯离开的驮鸽。
+
+## History
+
+据说是第 29 次远征军东进时打下的第一口井。远征军走了，井留下了。