feat: hardware binding modes, operator management, packaged SDK

- Hardware binding: License.HwBinding (none | fixed | firstActivation).
  firstActivation leaves the license unbound until the first activation,
  which claims the machine; afterwards it behaves like fixed. Legacy rows
  backfilled to fixed when a fingerprint was already set.
- Rebind: POST /panel/licenses/{id}/rebind moves a license to new
  hardware (or releases the binding), deactivating existing activations
  and re-signing a new version; 409 on revoked/expired. Operator or
  company admin. Audited, emits license.rebound.
- Operator management: list, invite, promote and demote operators
  (operator-only), guarding self-demotion and the last operator — until
  now a second operator could only be seeded directly into the database.
- SDK packaging: CertifiEd.Client is now a proper NuGet package (id,
  version, MIT license, README, XML docs, symbols) and gained the
  missing public XML documentation.

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Ofarandagon
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.