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/bus/__init__.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """DECNET ServiceBus — pub/sub notification substrate.
 
 The bus is the notification layer for DECNET's worker constellation.  The DB

decnet/bus/app.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Process-wide bus singleton for request-serving workers (API, SSE routes).
 
 A single connected :class:`~decnet.bus.base.BaseBus` shared across request

decnet/bus/base.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Bus abstractions: the :class:`Event` envelope and the :class:`BaseBus` ABC.
 
 Every transport (NATS, in-process fake, null) speaks this contract.  The

decnet/bus/factory.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Bus factory — selects a :class:`~decnet.bus.base.BaseBus` implementation.
 
 Dispatch key: the ``DECNET_BUS_TYPE`` environment variable.

decnet/bus/fake.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """In-process bus transports.
 
 * :class:`FakeBus` — real pub/sub semantics without touching a socket.  Used

decnet/bus/protocol.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Wire protocol for the DECNET bus UNIX-socket transport.
 
 Frame layout:

decnet/bus/publish.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Fire-and-forget publish helpers shared across every worker.
 
 Lifted out of ``decnet/mutator/engine.py`` once a second caller showed up

decnet/bus/topics.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Canonical topic hierarchy for the DECNET ServiceBus.
 
 Locked early so consumers can subscribe with stable wildcard patterns.

decnet/bus/unix_client.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """UNIX-socket client — :class:`UnixSocketBus` implementation of :class:`BaseBus`.
 
 Holds one open socket to the local :class:`~decnet.bus.unix_server.BusServer`.

decnet/bus/unix_server.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """UNIX-socket server for the DECNET bus.
 
 One :class:`BusServer` per host.  Accepts local connections on a UNIX-domain

decnet/bus/worker.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """``decnet bus`` worker entrypoint.
 
 Starts a :class:`~decnet.bus.unix_server.BusServer` on the configured UNIX