Name the sizes a node can ask for

Raw cpus and gpus are a property of the machines an installation has, so a node
written against a cluster quietly stops meaning anything when the cluster is
replaced. A node says "gpu-small" instead, and what that is stored here —
editable, and read again every time the node is built, so changing the flavor
changes what the next run gets.

Memory joins the schema properly (`ram`, in MB, accepting "2G"), along with
`duration_s` for how long a node is expected to take. That one is recorded and
shown and nothing else yet: a statement for whoever is planning around the node,
not a limit — the limit is still `timeout`.

A flavor and a number for the same thing is refused, compared by value so an
editor writing the whole object back with its defaults still round-trips. A name
nothing stores is refused at the save, which covers the canvas and `fluksio
sync` at once, and deleting one a node still asks for says which node.

Four sizes are seeded on an installation that has none, and never re-seeded:
re-adding one somebody deliberately removed is an argument nobody wins.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A6HeySA27EkGANZN95QySW

backend/fluksio/models.py

@@ -462,3 +462,55 @@ class RunArtifact(SQLModel, table=True):
         default_factory=lambda: datetime.now(UTC),
         sa_type=UTCDateTime,
     )
+
+
+# -----------------------------------------------------------------------------
+# Flavors
+# -----------------------------------------------------------------------------
+
+
+class FlavorBase(SQLModel):
+    """A named amount of machine, so a node can ask for one by name.
+
+    The point is not to save typing. Cores and megabytes are a property of the
+    machines an installation actually has, and they change when those machines
+    do — so a node saying "gpu-small" keeps meaning something after the cluster
+    is replaced, where a node saying 8 and 16384 quietly stops.
+    """
+
+    cpus: int = Field(default=1, ge=1)
+    gpus: int = Field(default=0, ge=0)
+    #: Megabytes. A flavor always says, which is what a node asking for one is
+    #: buying — the raw form leaves memory unstated and unaccounted.
+    ram: int = Field(default=2048, ge=1)
+    description: str = Field(default="", max_length=255)
+
+
+class Flavor(FlavorBase, table=True):
+    """A resource size somebody named, stored so nodes can refer to it."""
+
+    __tablename__ = "flavor"
+
+    name: str = Field(primary_key=True, max_length=64)
+
+
+class FlavorCreate(FlavorBase):
+    name: str = Field(max_length=64)
+
+
+class FlavorUpdate(SQLModel):
+    """Everything but the name: renaming would orphan the nodes that ask."""
+
+    cpus: int | None = Field(default=None, ge=1)
+    gpus: int | None = Field(default=None, ge=0)
+    ram: int | None = Field(default=None, ge=1)
+    description: str | None = Field(default=None, max_length=255)
+
+
+class FlavorPublic(FlavorBase):
+    name: str
+
+
+class FlavorsPublic(SQLModel):
+    data: list[FlavorPublic]
+    count: int