0.4.0 — settings card migrated to the DSH 0.1.7 seats

The settings card moved to the seats the DSH 0.1.7 line provides — host behaviour is unchanged.

• The card registers into plugins.bundle.config, keyed by the bundle package name (the seat dsh-client-ui-plugin-manager renders as the plugin's own page), instead of the removed settings.plugin.item.
• Settings reads and writes go through ctx.configForms.get('image-tiler') instead of the removed ctx.settingsScope, and inject is now configForms. The surface the card uses is unchanged: getSnapshot / subscribe / set(field, value) / unset(field), with status / value / user / writable in the snapshot.
• package.json now declares dsh.engines.dsh >= 0.1.7-rc.1: on an older host the removed seat fails silently — no error, the settings card simply never appears.
• Adds tests/client.test.mjs (7 dependency-free invariants) and a CHANGELOG; the full suite is 58 tests. Composition re-verified against DSH 0.1.7-rc.2 with the real CLI.

Old DSH (≤ 0.1.6 line): keep using 0.3.1.
npm: https://www.npmjs.com/package/@mengli114/dsh-image-tiler

设置卡片迁移到 DSH 0.1.7 的新 seat（plugins.bundle.config + ctx.configForms），宿主侧行为不变；旧版 DSH 请继续用 0.3.1。