feat(groups): schema 25 -- two profiles on one device can hold one group

The refusal `679d5249` added is gone, and with it the last reason it existed.

**The per-viewer field had to go first.** `ChatMessage.isUserMessage` was a boolean
about one reader stored on a row that belongs to the group: a transcript line is
deduped by the group event behind it, and `reconcileMarmotLine` lets the fresher row
win, so whichever profile indexed the event last decided whose message it looked
like. A member's own messages would draw as somebody else's and flip back when the
other profile caught up -- on every line in the room.

It is `senderIdentity` now, and `ChatMessage.isFrom(userPublicKey)` asks the
question. The identity is the fact about the message; whether it is yours is a
question only a reader can ask. Not derivable from `senderPublicKey`, which for a
Marmot line is the kind:445's ephemeral signer -- the same trap the comment on
`fromGroupEventResult` already records someone falling into. `answeredRequests` takes
the asking profile for the same reason: the other profile's approval is not this
one's to be credited with.

The backfill is exact, and exact for the reason the bug could not happen yet: the
boolean was only safe to store because a room belonged to one profile, so a line
marked as the user's was sent by that room's one member, and `ChatRoomMembership`
says who. `isUserMessage` is named by no index or constraint, so `DROP COLUMN` takes
it and `ChatMessage`'s three cascading children are untouched.

**Removing the refusal was not enough.** The Welcome branch keyed on the *room*, so a
Welcome that found one fell through and did nothing -- the accidental silent refusal
that `679d5249` was written to make legible in the first place. It asks about this
profile's membership now, and the body it guards already does the right thing for a
joiner: the room's upsert is idempotent, the bundle consumed is their own, the roster
is the group's, and `adopt` files a statement the group already signed.

`TYPE_WELCOME_REFUSED_OTHER_PROFILE` stays, written by nothing and still rendered.
Devices that ran the older build hold lines of that type, and a transcript that
cannot draw a line it is holding is worse than one drawing an obsolete notice.

`WelcomeForOtherProfileJvmTest` becomes `SecondProfileJoinsGroupJvmTest` and asserts
the opposite of what it used to: two memberships of one room, two distinct ratchet
states, the holder's untouched, no refusal line, and the key package spent like any
other join's.

1216 tests, 0 failures.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

composeApp/schemas/press.mantra.compose.database.MantraDatabase/24.json

@@ -2,7 +2,7 @@
   "formatVersion": 1,
   "database": {
     "version": 24,
-    "identityHash": "1e328aab136444e802ffa7443e06ebe6",
+    "identityHash": "c99c92c14e98a35c2d2a13118bc1f727",
     "entities": [
       {
         "tableName": "BroadcastNostrEventReceipt",
@@ -282,7 +282,7 @@
       },
       {
         "tableName": "ChatMessage",
-        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `senderPublicKey` TEXT NOT NULL, `isUserMessage` INTEGER NOT NULL, `giftWrapPayloadId` TEXT, `marmotGroupEventId` TEXT, `marmotInnerEventId` TEXT, `chatRoomId` TEXT NOT NULL, `replyToMessageId` INTEGER, `quotedMessageId` INTEGER, `content` TEXT NOT NULL, `messageType` TEXT NOT NULL, `directMessageRecipientPublicKey` TEXT, `frostSigningSessionId` TEXT, `dkgSessionId` TEXT, `createdAt` INTEGER NOT NULL, `updatedAt` INTEGER NOT NULL, `savedAt` INTEGER NOT NULL, `viewedAt` INTEGER, `deletedAt` INTEGER, FOREIGN KEY(`chatRoomId`) REFERENCES `ChatRoom`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`giftWrapPayloadId`) REFERENCES `GiftWrapPayload`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`marmotGroupEventId`) REFERENCES `MarmotGroupEvent`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`marmotInnerEventId`) REFERENCES `MarmotInnerEvent`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE )",
+        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `senderPublicKey` TEXT NOT NULL, `senderIdentity` TEXT, `giftWrapPayloadId` TEXT, `marmotGroupEventId` TEXT, `marmotInnerEventId` TEXT, `chatRoomId` TEXT NOT NULL, `replyToMessageId` INTEGER, `quotedMessageId` INTEGER, `content` TEXT NOT NULL, `messageType` TEXT NOT NULL, `directMessageRecipientPublicKey` TEXT, `frostSigningSessionId` TEXT, `dkgSessionId` TEXT, `createdAt` INTEGER NOT NULL, `updatedAt` INTEGER NOT NULL, `savedAt` INTEGER NOT NULL, `viewedAt` INTEGER, `deletedAt` INTEGER, FOREIGN KEY(`chatRoomId`) REFERENCES `ChatRoom`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`giftWrapPayloadId`) REFERENCES `GiftWrapPayload`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`marmotGroupEventId`) REFERENCES `MarmotGroupEvent`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`marmotInnerEventId`) REFERENCES `MarmotInnerEvent`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE )",
         "fields": [
           {
             "fieldPath": "id",
@@ -297,10 +297,9 @@
             "notNull": true
           },
           {
-            "fieldPath": "isUserMessage",
-            "columnName": "isUserMessage",
-            "affinity": "INTEGER",
-            "notNull": true
+            "fieldPath": "senderIdentity",
+            "columnName": "senderIdentity",
+            "affinity": "TEXT"
           },
           {
             "fieldPath": "giftWrapPayloadId",
@@ -6215,7 +6214,7 @@
     ],
     "setupQueries": [
       "CREATE TABLE IF NOT EXISTS room_master_table (id INTEGER PRIMARY KEY,identity_hash TEXT)",
-      "INSERT OR REPLACE INTO room_master_table (id,identity_hash) VALUES(42, '1e328aab136444e802ffa7443e06ebe6')"
+      "INSERT OR REPLACE INTO room_master_table (id,identity_hash) VALUES(42, 'c99c92c14e98a35c2d2a13118bc1f727')"
     ]
   }
 }