chore: license Ekklesia under AGPL-3.0-only

Ekklesia is open source under the GNU Affero General Public License, version 3
only. Module Package v1 (#66) bundles Ekklesia's SDK and contracts into
distributable module packages, so the platform needs an explicit license
before such artifacts are distributed.

- LICENSE: the GNU AGPL v3 text, verbatim from
  https://www.gnu.org/licenses/agpl-3.0.txt
  (sha256 0d96a4ff68ad6d4b6f1f30f713b18d5184912ba8dd389f86aa7710db079abcb0).
- "license": "AGPL-3.0-only" in the root package.json and every Ekklesia
  workspace package (13 packages), the module template included. Nothing else in
  any manifest changed.
- README: a License section replacing the "no license selected yet" placeholder:
  AGPL v3 only, source available under its terms, section 13's network-use
  obligation, and the policy that official Ekklesia modules use AGPL-3.0-only.
- Module template README and module development guide: the template declares
  the license; Module Package v1 does not yet record a module's own license,
  which needs a format change under ADR 0049.

AGPL-3.0-only, not -or-later: the decision is AGPL-3.0, and nothing in the
repository grants later versions. No runtime, ADR, package-format, Signage, or
instance change. The packaged template is byte-identical before and after.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

templates/module/package.json

@@ -1,6 +1,7 @@
 {
   "name": "@ekklesia/module-template",
   "version": "0.1.0",
+  "license": "AGPL-3.0-only",
   "private": true,
   "type": "module",
   "files": [