chore: relicense to AGPL-3.0-or-later and add SPDX headers

Replaces LICENSE (GPLv3 -> AGPLv3) and prepends
`SPDX-License-Identifier: AGPL-3.0-or-later` to every source file
across decnet/, decnet_web/, tests/, scripts/, and tools/.

Rationale: closes the GPLv3 ASP loophole so any party operating a
modified DECNET as a network service must offer their modified
source. Personal copyright (Samuel Paschuan) + inbound=outbound
contributions make a future unilateral relicense infeasible.

- LICENSE: full AGPL-3.0 text (gnu.org/licenses/agpl-3.0.txt)
- COPYRIGHT: project copyright notice
- tools/add_spdx_headers.py: idempotent header injector
  (shebang- and PEP 263-aware)

Touches 1565 source files (.py, .ts, .tsx, .js, .jsx, .css, .sh).
No behavior change; comments only.

decnet/orchestrator/drivers/__init__.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Activity drivers for the orchestrator.
 
 Concrete drivers register dispatch in :func:`get_driver_for`.  Same

decnet/orchestrator/drivers/base.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Driver ABC for orchestrator actions.
 
 Each concrete driver (SSH, Email, future HTTP/SMB/MySQL) maps one

decnet/orchestrator/drivers/email.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Email driver — pluggable-LLM EML generation + decky-side delivery.
 
 One :class:`EmailAction` becomes one EML written into the mail decky's

decnet/orchestrator/drivers/smtp_relay.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """SMTP probe-relay driver.
 
 Forwards the attacker's first probe email via the master's real internet

decnet/orchestrator/drivers/ssh.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """MVP SSH-flavoured driver.
 
 Two action shapes: