[roomcomments] implement basic room comments

apps/roomcomments/migrations/0001_room_comment.sql

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+-- Room comments — the notes a player leaves pinned in a room's scene, which everyone
+-- standing in that subroom sees floating at the position they were dropped. Generated from
+-- packages/domain/src/room-comments-db.ts (ROOM_COMMENT_SCHEMA_DDL) — keep in sync.
+--
+-- Columns rather than a JSON blob (the `club_announcement` pattern rather than the
+-- `room`/`club` one): a comment is six scalars and a point, none of it a client-shaped
+-- document that has to survive round-tripping, and the room/subroom pair has to be
+-- queryable.
+
+-- `comment_id` is an ordinary autoincrement integer, and it is the CURSOR the read endpoint
+-- pages on (`GET /comments/get/:roomId?minId=`), so it has to be monotonic per insert.
+-- AUTOINCREMENT rather than a bare rowid alias for exactly that reason: a deleted comment's
+-- id must never be handed out again, or a client polling with `minId` would skip the
+-- comment that reused it.
+--
+-- The position is three REALs, not the strings the form body carries. The client posts a
+-- C# float's shortest round-trip text (`positionX=-0.4979804`) but reads the response back
+-- as a NUMBER — `"PositionX": "1.5"` fails its parser — and a float64 holds those 7-9
+-- significant digits exactly, so the text that arrives is the text that goes back out.
+CREATE TABLE IF NOT EXISTS room_comment (
+  comment_id INTEGER PRIMARY KEY AUTOINCREMENT,
+  room_id INTEGER NOT NULL,
+  subroom_id INTEGER NOT NULL,
+  player_id INTEGER NOT NULL,
+  style INTEGER NOT NULL DEFAULT 0,
+  message TEXT NOT NULL DEFAULT '',
+  position_x REAL NOT NULL DEFAULT 0,
+  position_y REAL NOT NULL DEFAULT 0,
+  position_z REAL NOT NULL DEFAULT 0,
+  created_at TEXT NOT NULL
+  );
+
+-- The read is always "this room, newer than this id, newest first" — one index covers the
+-- filter and the ordering together.
+CREATE INDEX IF NOT EXISTS idx_room_comment_room ON room_comment (room_id, comment_id);