implement paywall (#161)

* implement core foundation

* inject deps

* fix incorrect migration

* tail migration

* use transaction for migration

* fix: inject deps for tests

* cleanup billing management for admin

* upgrade stripe sdk to v85

* set price env variables

* cleanup billing management

* allow multiple dev windows

* fix: settings scroll

* feat: show nice video thumbnail in listview

* feat: implement freemium restrictions

* remove unnecessary comments

* refactor

* docs

* format

* tweak network settings better hierarchy

go/internal/billing/usage_models.go

@@ -0,0 +1,15 @@
+package billing
+
+import "time"
+
+// FreemiumDailyLimit is the per-network daily cap on usage,
+// agnostic of the units that this refer to. This is only relevant for the "free" plan.
+const FreemiumDailyLimit = 50
+
+// Usage describes a network's current freemium quota state for today.
+type Usage struct {
+	Plan    Plan      `json:"plan"`
+	Used    int       `json:"used"`
+	Limit   *int      `json:"limit"` // nil = unlimited (pro)
+	ResetAt time.Time `json:"reset_at"`
+}