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>

README.md

@@ -172,6 +172,33 @@ OpenSC relies on PCSC driver, which reads a list (`Info.plist`) that contains a
 - Use the pure-browser online [Pico Commissioner](https://www.picokeys.com/pico-commissioner/ "Pico Commissioner") that commissions the Pico Key on-the-fly without external tools.
 - Build and configure the project with the proper VID/PID with `USB_VID` and `USB_PID` parameters in `CMake` (see [Build section](#build "Build section")). Note that you cannot distribute the patched/compiled binary if you do not own the VID/PID or have an explicit authorization.
 
+## License and Commercial Use
+
+This project is available under two editions:
+
+**Community Edition (FOSS)**
+- Released under the GNU Affero General Public License v3 (AGPLv3).
+- You are free to study, modify, and run the code, including for internal evaluation.
+- If you distribute modified binaries/firmware, OR if you run a modified version of this project as a network-accessible service, you must provide the corresponding source code to the users of that binary or service, as required by AGPLv3.
+- No warranty. No SLA. No guaranteed support.
+
+**Enterprise / Commercial Edition**
+- Proprietary license for organizations that want to:
+  - run this in production with multiple users/devices,
+  - integrate it into their own product/appliance,
+  - enforce corporate policies (PIN policy, admin/user roles, revocation),
+  - and *not* be required to publish derivative source code.
+- Includes access to enterprise-only features (bulk provisioning, multi-user policy controls, device inventory & revocation, custom attestation/identity), official signed builds, and an onboarding call.
+
+Typical licensing models:
+- Internal use (within one legal entity).
+- Redistribution / OEM (shipping this as part of your product).
+
+For commercial licensing and enterprise features, email pol@henarejos.me
+Subject: `ENTERPRISE LICENSE <your company name>`
+
+See `ENTERPRISE.md` for details.
+
 ## Credits
 Pico OpenPGP uses the following libraries or portion of code:
 - MbedTLS for cryptographic operations.