licence: relicense MIT -> AGPL-3.0-or-later

lectio was MIT, which let anyone take it closed. The concern is not people
selling it -- no licence stops that, and the AGPL does not try to -- but
someone building a proprietary product on it and giving nothing back.

Plain GPL would leave the obvious hole open: lectio-web is a network
service, and hosting is not distribution, so a modified lectio-web could be
run as a paid subscription API without ever publishing a line. AGPL section
13 closes exactly that.

LICENSE is the verbatim FSF text. README carries the standard notice.

Section 13 requires a modified network-reachable version to PROMINENTLY
offer its source to the users interacting with it, so the offer ships with
the code rather than living only in a file nobody fetches:

  - GET /source          plain text, no template or config dependency, so
                         it answers even when something else is broken
  - page footers         every full page (fragments render inside one)
  - JSON envelope        "source" / "license"
  - iCal header          X-LECTIO-SOURCE / X-LECTIO-LICENSE

The feed fields are not redundant: an /api/calendar.json consumer or an
.ics subscriber never loads a page, so the footer alone would miss them.

config.SourceURL is the single source of truth, and says in its comment
that a fork running as a service must repoint it -- an offer that leads to
someone else's code is not an offer.

Tests pin all of it. This is a licence obligation, not a feature, so it
should fail loudly if a later change drops it.

4 files changed, 10 insertions, 0 deletions

diff --git a/internal/web/templates/bookmarks.html b/internal/web/templates/bookmarks.html
index efc988a..770c73a 100644
--- a/internal/web/templates/bookmarks.html
+++ b/internal/web/templates/bookmarks.html
@@ -46,5 +46,7 @@
   {{end}}
 
 </div>
+
+<footer class="licence"><a href="/source">source</a> · AGPL-3.0-or-later</footer>
 </body>
 </html>
diff --git a/internal/web/templates/index.html b/internal/web/templates/index.html
index 762ed7b..b99725d 100644
--- a/internal/web/templates/index.html
+++ b/internal/web/templates/index.html
@@ -90,5 +90,9 @@
   <div id="pane">{{.Reading}}</div>
 
 </div>
+
+{{/* AGPL-3.0 §13: the source offer must be visible to anyone using this
+     server over a network, so it sits on every full page, not just here. */}}
+<footer class="licence"><a href="/source">source</a> · AGPL-3.0-or-later</footer>
 </body>
 </html>
diff --git a/internal/web/templates/reader.html b/internal/web/templates/reader.html
index ef144cc..36cc8a1 100644
--- a/internal/web/templates/reader.html
+++ b/internal/web/templates/reader.html
@@ -83,5 +83,7 @@
          onchange="document.body.classList.toggle('mono', this.checked)"> {{.L.Mono}}</label>
 
 </div>
+
+<footer class="licence"><a href="/source">source</a> · AGPL-3.0-or-later</footer>
 </body>
 </html>
diff --git a/internal/web/templates/settings.html b/internal/web/templates/settings.html
index f4fae47..3ae2f41 100644
--- a/internal/web/templates/settings.html
+++ b/internal/web/templates/settings.html
@@ -104,5 +104,7 @@
   </form>
 
 </div>
+
+<footer class="licence"><a href="/source">source</a> · AGPL-3.0-or-later</footer>
 </body>
 </html>