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/ttp/__init__.py

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

tests/api/ttp/conftest.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Shared helpers for TTP API contract tests (E.2.8).
 
 The base ``tests/api/conftest.py`` already provides ``client``,

tests/api/ttp/test_get_endpoints.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """E.2.8 — GET endpoint shape + auth contract for /api/v1/ttp/*.
 
 The TTP router landed at E.1.9 (contract phase) returning typed

tests/api/ttp/test_response_schemas.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """E.2.8 — Response-schema stability via golden fixtures.
 
 The OpenAPI schema for each TTP endpoint is captured under

tests/api/ttp/test_rules_catalogue.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """GET /api/v1/ttp/rules returns the live rule catalogue.
 
 Pins the runtime fix that replaced the contract-phase ``return []``

tests/api/ttp/test_rules_state.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """E.2.8 — Admin-only mutation endpoints for /api/v1/ttp/rules/{id}/state.
 
 The two mutation endpoints (POST / DELETE) carry the rule

tests/api/ttp/test_tag_details.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """GET /api/v1/ttp/tags/by-{scope}/{uuid}/{technique_id}.
 
 Pins the operator inspector endpoint that surfaces the rule engine's