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.

tests/fleet/__init__.py

@@ -0,0 +1 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later

tests/fleet/test_archetypes.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Tests for machine archetypes and the amount= expansion feature.
 """

tests/fleet/test_auto_spawn.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Auto-spawn of forwarder from `decnet agent` (and listener from
 `decnet swarmctl`, added in a later patch).
 

tests/fleet/test_composer.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Tests for the composer — verifies BASE_IMAGE injection and distro heterogeneity.
 """

tests/fleet/test_deployer.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Tests for decnet/engine/deployer.py
 

tests/fleet/test_fleet.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Tests for decnet/fleet.py — fleet builder logic.
 

tests/fleet/test_fleet_singleton.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Tests for fleet_singleton service behavior.
 

tests/fleet/test_reconciler.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Tests for decnet.fleet.reconciler — pure-function reconcile pass.
 
 Uses a fake repository (in-memory dict) and a stub docker client so the

tests/fleet/test_reconciler_worker.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Worker shutdown smoke test for fleet_reconciler_worker.
 
 The reconcile logic itself is exercised in test_reconciler.py.  This file