refactor(board): delete old board routes, absorb slackHandle into profile PATCH

- Delete server/api/members/me/board.patch.js and server/api/board/suggestions.get.js
- Add boardSlackHandle to memberProfileUpdateSchema; remove boardPrivacy
- profile.patch.js: write boardSlackHandle -> board.slackHandle; drop boardPrivacy
- Remove privacy.board field from Member model
- onboarding/status.get.js: hasProfileTags now requires only craftTags; hasEngagedBoard uses BoardPost.exists
- onboarding/track.post.js: graduation check uses BoardPost.exists instead of board.topics elemMatch
- members/[id].get.js and directory.get.js: reduce board response to slackHandle only; drop connectionTag and peerSupport filters

server/models/member.js

@@ -118,11 +118,6 @@ const memberSchema = new mongoose.Schema({
       enum: ["public", "members", "private"],
       default: "members",
     },
-    board: {
-      type: String,
-      enum: ["public", "members", "private"],
-      default: "members",
-    },
   },
 
   notifications: {