big update: added reactions, groups, media share

server/internal/store/migrations/0003_reactions.sql

@@ -0,0 +1,9 @@
+-- 0003_reactions.sql
+CREATE TABLE IF NOT EXISTS message_reactions (
+    message_id BIGINT NOT NULL REFERENCES messages(id) ON DELETE CASCADE,
+    user_id    BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    emoji      TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    PRIMARY KEY (message_id, user_id, emoji)
+);
+CREATE INDEX IF NOT EXISTS idx_reactions_message ON message_reactions(message_id);