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/alembic/versions/c7e2b9f34a15_flavor_table.py

@@ -0,0 +1,42 @@
+"""flavor
+
+A named amount of machine — cores, cards and memory — so a node can ask for one
+by name. Seeded with a few sizes on first start, and editable afterwards: what
+"gpu-small" means is a property of the machines an installation has, and those
+change.
+
+Revision ID: c7e2b9f34a15
+Revises: b3f1a7c50d92
+Create Date: 2026-08-27
+
+"""
+
+import sqlalchemy as sa
+import sqlmodel.sql.sqltypes
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "c7e2b9f34a15"
+down_revision = "b3f1a7c50d92"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_table(
+        "flavor",
+        sa.Column("name", sqlmodel.sql.sqltypes.AutoString(length=64), nullable=False),
+        sa.Column("cpus", sa.Integer(), nullable=False),
+        sa.Column("gpus", sa.Integer(), nullable=False),
+        sa.Column("ram", sa.Integer(), nullable=False),
+        sa.Column(
+            "description",
+            sqlmodel.sql.sqltypes.AutoString(length=255),
+            nullable=False,
+        ),
+        sa.PrimaryKeyConstraint("name"),
+    )
+
+
+def downgrade():
+    op.drop_table("flavor")