refactor(shared): strip cryptographic device provisioning (now telemetry-only)

devices rows no longer carry public_key for crypto purposes. The whole
per-device key API surface (provisionNewDevice, loadDevicePrivateKey,
saveDevicePrivateKey, forgetDevicePrivateKey, restoreDeviceFromServerRecord)
is removed; registerDevice now records {name, platform} only. SQL drops the
NOT NULL on devices.public_key so future telemetry rows can omit it.

Note: SQL not applied locally - push via pnpm prod:migrate when ready.

packages/db-types/src/index.ts

@@ -118,7 +118,7 @@ export type Database = {
           last_seen_at: string
           name: string
           platform: Database["public"]["Enums"]["device_platform"]
-          public_key: string
+          public_key: string | null
           user_id: string
         }
         Insert: {
@@ -127,7 +127,7 @@ export type Database = {
           last_seen_at?: string
           name: string
           platform: Database["public"]["Enums"]["device_platform"]
-          public_key: string
+          public_key?: string | null
           user_id: string
         }
         Update: {
@@ -136,7 +136,7 @@ export type Database = {
           last_seen_at?: string
           name?: string
           platform?: Database["public"]["Enums"]["device_platform"]
-          public_key?: string
+          public_key?: string | null
           user_id?: string
         }
         Relationships: []