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/topology/__init__.py

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

tests/api/topology/test_child_crud.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Phase 3 Step 4 — child CRUD: LAN / decky / edge."""
 from __future__ import annotations
 

tests/api/topology/test_events_stream.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """SSE events stream — GET /topologies/{id}/events (DEBT-030)."""
 from __future__ import annotations
 

tests/api/topology/test_models.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Phase 3 Step 1 — parity between repo dict output and Pydantic DTOs.
 
 These tests pin the contract that repo-hydrated dicts deserialize

tests/api/topology/test_mutations.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Phase 3 Step 5 — live mutation queue endpoints."""
 from __future__ import annotations
 

tests/api/topology/test_personas_api.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Per-topology persona endpoints — GET/PUT /topologies/{id}/personas."""
 from __future__ import annotations
 

tests/api/topology/test_reads.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Phase 3 Step 2 — read endpoints: list / get / status-events / catalog."""
 from __future__ import annotations
 

tests/api/topology/test_writes.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Phase 3 Step 3 — write endpoints: create / delete / deploy."""
 from __future__ import annotations