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/geoip/__init__.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 GeoIP enrichment — maps attacker IPs to country codes for attacker intelligence.
 

decnet/geoip/base.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """GeoIP provider protocol.
 
 Concrete providers (:mod:`decnet.geoip.rir`, future ``dbip``, ``maxmind``)

decnet/geoip/factory.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """GeoIP provider factory.
 
 Dispatch key: ``DECNET_GEOIP_PROVIDER`` (default ``rir``). Lazy singleton,

decnet/geoip/lookup.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Provider-agnostic country lookup.
 
 A :class:`Lookup` is a frozen, sorted array of (start_ip, end_ip, cc)

decnet/geoip/paths.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Filesystem layout for GeoIP data.
 
 ``GEOIP_ROOT`` is where providers drop their raw files and cache indexes.

decnet/geoip/ptr.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Reverse DNS (PTR record) lookup for attacker IPs.
 
 Colocated with ``decnet.geoip`` because the shape matches: take an IP,

decnet/geoip/rir/__init__.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """RIR delegated-stats provider.
 
 Free, offline, no license: each Regional Internet Registry publishes a

decnet/geoip/rir/fetch.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """RIR delegated-stats download.
 
 Five public files, ~5 MB total. Pulled over HTTPS with a generic

decnet/geoip/rir/parse.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Parser for RIR ``delegated-*-extended`` files.
 
 Line shape (the bits we care about)::

decnet/geoip/rir/provider.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """RIR provider — orchestrates fetch + parse into a :class:`Lookup`."""
 from __future__ import annotations