Prompt suggestions on the new-chat screen

A blank composer is the least helpful thing a chat client can show someone
who has just installed one. Three cards now sit under the empty state, and
an administrator manages them at /admin/suggestions.

Clicking a card fills the composer and stops there. It deliberately does not
send: every default ends mid-sentence, because a card is a starting point
rather than a question somebody already asked, and the caret lands where the
person has to start typing.

Seeding is guarded by a settings flag, not by "is the table empty" --
otherwise an administrator who decided against them would get all three back
on every restart. Capped at twelve, six shown: past a dozen this is a menu,
and a menu on the empty screen is a worse blank page than a blank page.

The cards are gated on there being no chat at all, not on the thread being
empty. An empty chat someone opened on purpose already has a model and a
prompt chosen.

Also fixes a pre-existing bug the position test caught. Both this and
_refresh_models wrote `coalesce(max(position), -1) or -1`, and position 0 is
falsy -- so the second row landed back on 0 on top of the first. The
coalesce was already doing that job; the `or` was undoing it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/db/models/__init__.py

@@ -41,6 +41,7 @@ from lembas.db.models.library import (
     chat_knowledge_bases,
 )
 from lembas.db.models.setting import Setting
+from lembas.db.models.suggestion import Suggestion
 from lembas.db.models.user import (
     ROLE_ADMIN,
     ROLE_PENDING,
@@ -85,6 +86,7 @@ __all__ = [
     "Share",
     "Skill",
     "SkillRevision",
+    "Suggestion",
     "User",
     "chat_knowledge_bases",
     "model_groups",

src/lembas/db/models/suggestion.py

@@ -0,0 +1,32 @@
+"""Starting points offered on the new-chat screen."""
+
+from __future__ import annotations
+
+from sqlalchemy import Boolean, Integer, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from lembas.db.base import Base, Timestamps, UUIDPrimaryKey
+
+
+class Suggestion(UUIDPrimaryKey, Timestamps, Base):
+    """One card on the empty chat screen.
+
+    Instance-wide rather than per-user: these are what an administrator wants
+    people to start with, the same way the instance system prompt is. There is
+    no owner_id and therefore nothing for `sharing` to decide.
+    """
+
+    __tablename__ = "suggestions"
+
+    name: Mapped[str] = mapped_column(String(120), nullable=False)
+    description: Mapped[str] = mapped_column(String(300), default="")
+    # What lands in the composer. Deliberately not sent on its own: it usually
+    # ends mid-sentence, because a card is a starting point rather than a
+    # question somebody already asked.
+    prompt: Mapped[str] = mapped_column(Text, default="")
+
+    enabled: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    position: Mapped[int] = mapped_column(Integer, default=0, nullable=False)
+
+    def __repr__(self) -> str:
+        return f"<Suggestion {self.name}>"