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.

scripts/profile/aggregate_requests.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Aggregate pyinstrument request profiles from ./profiles/*.html.
 

scripts/profile/classify_usage.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Classify the shape of a memray usage_over_time.csv as plateau, climb,
 or climb-and-drop. Operates on the `memory_size_bytes` column.

scripts/profile/cprofile-cli.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# SPDX-License-Identifier: AGPL-3.0-or-later
 # Run a `decnet` subcommand under cProfile and write a .prof file for snakeviz.
 # Usage: scripts/profile/cprofile-cli.sh services
 #        scripts/profile/cprofile-cli.sh status

scripts/profile/memray-api.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# SPDX-License-Identifier: AGPL-3.0-or-later
 # Run the DECNET API under memray to capture an allocation profile.
 # Stop with Ctrl-C; then render with `memray flamegraph <bin>`.
 set -euo pipefail

scripts/profile/pyspy-attach.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# SPDX-License-Identifier: AGPL-3.0-or-later
 # Attach py-spy to the running DECNET uvicorn worker(s) and record a flamegraph.
 # Requires sudo on Linux because of kernel.yama.ptrace_scope=1 by default.
 set -euo pipefail

scripts/profile/view.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# SPDX-License-Identifier: AGPL-3.0-or-later
 # Open the newest profile artifact in the right viewer.
 #
 # Usage: