Relicense project under the GNU Affero General Public License v3 (AGPLv3)

and add the Enterprise / Commercial licensing option.

Main changes:
- Replace GPLv3 headers with AGPLv3 headers in source files.
- Update LICENSE file to the full AGPLv3 text.
- Add ENTERPRISE.md describing the dual-licensing model:
  * Community Edition: AGPLv3 (strong copyleft, including network use).
  * Enterprise / Commercial Edition: proprietary license for production /
    multi-user / OEM use without the obligation to disclose derivative code.
- Update README with a new "License and Commercial Use" section pointing to
  ENTERPRISE.md and clarifying how companies can obtain a commercial license.

Why this change:
- AGPLv3 ensures that modified versions offered as a service or deployed
  in production environments must provide corresponding source code.
- The Enterprise / Commercial edition provides organizations with an
  alternative proprietary license that allows internal, large-scale, or OEM
  use (bulk provisioning, policy enforcement, inventory / revocation,
  custom attestation, signed builds) without AGPL disclosure obligations.

This commit formally marks the first release that is dual-licensed:
AGPLv3 for the Community Edition and a proprietary commercial license
for Enterprise customers.

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

src/fs/mman.h

@@ -1,14 +1,27 @@
 /*
- * sys/mman.h
- * mman-win32
+ * This file is part of the Pico Keys SDK distribution (https://github.com/polhenarejos/pico-keys-sdk).
+ * Copyright (c) 2022 Pol Henarejos.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
  */
 
+
 #ifndef _SYS_MMAN_H_
 #define _SYS_MMAN_H_
 
-#ifndef _WIN32_WINNT		// Allow use of features specific to Windows XP or later.                   
+#ifndef _WIN32_WINNT		// Allow use of features specific to Windows XP or later.
 #define _WIN32_WINNT 0x0501	// Change this to the appropriate value to target other versions of Windows.
-#endif						
+#endif
 
  /* All the headers include this file. */
 #ifndef _MSC_VER