fix(community-poi): default acceptsContributions to true

`acceptsContributions: z.boolean().optional()` was stored as `false`
when the field was absent from frontmatter, so @nuxt/content's
generated column made every POI evaluate `acceptsContributions === false`
— flagging all three real community projects as "showcase only" with
the lock badge on the overview.

Switch to `z.boolean().default(true)`: the SQL column is now
`BOOLEAN DEFAULT true`, so a POI is community-contributable unless it
explicitly opts out with `acceptsContributions: false`. Verified the
rebuilt content DB stores `true` for all three POIs (de + en).

https://claude.ai/code/session_01TWED5ZjQD6uv434RqTBaY2

Author: claude

content.config.ts

@@ -238,7 +238,10 @@ const communityPoiSchema = withI18nMeta(z.object({
     startedAt: z.coerce.date().optional(),
     updatedAt: z.coerce.date().optional(),
     forumUrl: z.string().url().optional(),
-    acceptsContributions: z.boolean().optional()
+    // Defaults to true: a POI is community-contributable unless it explicitly
+    // opts out. An `.optional()` boolean gets stored as `false` when absent,
+    // which would wrongly flag every POI as showcase-only.
+    acceptsContributions: z.boolean().default(true)
   }))
 
 export default defineContentConfig({