feat: persist scaling policies to Postgres

Adds scaling_policies table and wires the autoscaler: upsert on every
SetScalingPolicy (including delete-as-disable), LoadPolicies hydrates
policies + service states at boot. Persist failures are logged, never
fatal — in-memory state stays authoritative.

Verified live: policy written on POST, survives a full backend restart,
service state re-registers at min_replicas. Also gofmt-fixes the
drifted databases.go struct tags.

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/migrations_goose/20260921000000_scaling_policies.sql

@@ -0,0 +1,20 @@
+-- +goose Up
+CREATE TABLE IF NOT EXISTS scaling_policies (
+    service_id          uuid PRIMARY KEY REFERENCES services(id) ON DELETE CASCADE,
+    min_replicas        integer NOT NULL DEFAULT 1,
+    max_replicas        integer NOT NULL DEFAULT 1,
+    target_cpu          double precision NOT NULL DEFAULT 0,
+    target_memory       double precision NOT NULL DEFAULT 0,
+    scale_up_cooldown   bigint NOT NULL DEFAULT 0,
+    scale_down_cooldown bigint NOT NULL DEFAULT 0,
+    scale_up_step       integer NOT NULL DEFAULT 1,
+    scale_down_step     integer NOT NULL DEFAULT 1,
+    metrics             jsonb,
+    thresholds          jsonb,
+    enabled             boolean NOT NULL DEFAULT true,
+    cost_optimization   jsonb,
+    updated_at          timestamptz NOT NULL DEFAULT now()
+);
+
+-- +goose Down
+DROP TABLE IF EXISTS scaling_policies;