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/asn/__init__.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 IP-to-ASN enrichment — maps attacker IPs to BGP-announced AS numbers and
 org names for attacker intelligence.

decnet/asn/base.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """ASN provider protocol — mirror of :mod:`decnet.geoip.base`.
 
 Concrete providers (e.g. :mod:`decnet.asn.iptoasn`) implement this.

decnet/asn/factory.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """ASN provider factory — mirror of :mod:`decnet.geoip.factory`.
 
 Dispatch key: ``DECNET_ASN_PROVIDER`` (default ``iptoasn``). Lazy

decnet/asn/iptoasn/__init__.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """iptoasn.com IP→ASN provider.
 
 Daily-refreshed gzipped TSV dump of the global BGP table, derived from

decnet/asn/iptoasn/fetch.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """iptoasn.com bulk dump download.
 
 One file: ``ip2asn-v4.tsv.gz``, ~5 MB compressed, refreshed daily.

decnet/asn/iptoasn/parse.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Parser for the iptoasn.com ``ip2asn-v4.tsv`` dump.
 
 Line shape (gzipped, one row per BGP-announced prefix)::

decnet/asn/iptoasn/provider.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """iptoasn provider — orchestrates fetch + parse into an :class:`AsnLookup`.
 
 Mirrors :class:`decnet.geoip.rir.provider.RirProvider` exactly: fetch,

decnet/asn/lookup.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Provider-agnostic IP→ASN lookup.
 
 A :class:`AsnLookup` is a frozen, sorted array of ``(start_ip,

decnet/asn/paths.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """Filesystem layout for ASN data — mirror of :mod:`decnet.geoip.paths`.
 
 ``ASN_ROOT`` is where providers drop their raw files and cache indexes.