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/api/fleet/__init__.py

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

tests/api/fleet/test_deploy_additive.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """POST /deckies/deploy additive vs replace_fleet semantics.
 
 Default behaviour (replace_fleet=False) appends the INI to the existing

tests/api/fleet/test_deploy_automode.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """POST /deckies/deploy auto-mode: master + swarm hosts → shard to workers."""
 from __future__ import annotations
 

tests/api/fleet/test_get_deckies.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 import pytest
 import httpx
 from hypothesis import given, settings, strategies as st

tests/api/fleet/test_lifecycle_endpoint.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """GET /deckies/lifecycle?ids=… — poll endpoint for the wizard."""
 from __future__ import annotations
 

tests/api/fleet/test_mutate_decky.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Tests for the mutate decky API endpoint — now 202 fire-and-forget.
 

tests/api/fleet/test_mutate_interval.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Tests for the mutate interval API endpoint.
 """