docs: add ADR for pathway credentials

docs/openedx_learning/decisions/0007-pathway-credentials.rst

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+.. _openedx-learning-adr-0007:
+
+7. Pathway Credentials
+======================
+
+Status
+------
+
+Draft
+
+Context
+-------
+
+Learners who complete a Pathway should receive a certificate, in the same way as the built-in Open edX course
+certificates. Individual courses inside a Pathway keep their existing course certificates unchanged; this decision is
+only about the Pathway-level credential.
+
+Decisions
+---------
+
+1. **Earning rule.** A learner earns the Pathway certificate by fulfilling all Items in the Pathway. In the MVP that
+   means passing every course in the Pathway, where "passing" is dictated by each course's own grading policy. There
+   are no Pathway-level grades, thresholds, or enrollment modes.
+
+2. **Automatic issuance via signals.** The Pathways app listens for the Django signals the platform already emits when
+   a learner's course passing status changes. On each relevant signal, it re-evaluates the learner's Item fulfillment
+   for any enrolled Pathways containing that course, and issues the certificate as soon as all Items are fulfilled.
+   No manual issuing step is required.
+
+3. **Configuration in Django admin.** Pathway certificates are configured in the Django admin, not in Studio. A
+   certificate configuration can be created, previewed, edited, and deleted while inactive; it must be activated
+   before certificates are issued. Configuration includes the issuing organization and 1–4 signatories (name, title,
+   organization, signature image).
+
+4. **Rendering.** An issued certificate is rendered as an HTML page (printable by the learner), analogous to course
+   certificates. W3C Verifiable Credentials / Open Badges will not be supported in the MVP.
+
+5. **Issued certificates are records.** An issued certificate stores everything needed to display it later: recipient
+   name, Pathway name, issuer, signatories, the criteria met (the list of courses passed), and the date earned. It
+   remains valid and viewable even if the Pathway is later updated or archived.
+
+6. **Events.** Issuing a certificate emits an event, so that instances can report on credentials (e.g. in Aspects).
+
+.. Run `dot -Tsvg images/pathway-credentials.dot > images/pathway-credentials.svg` to regenerate the diagram after
+   making changes to `images/pathway-credentials.dot`.
+
+.. image:: images/pathway-credentials.svg
+   :alt: Pathway certificate issuance flow
+   :width: 100%
+
+Consequences
+------------
+
+- Because issuance uses the existing platform signals, no polling or batch jobs are needed for the typical flow.
+- Since certificates are self-contained records, later edits to the Pathway or its certificate configuration never
+  alter what a learner already earned.
+- Interaction-progress-based criteria, per-course credential rules, badges/microcredentials, and verifiable
+  credentials are all explicitly out of scope and can be layered on later without changing the basics of this design.

docs/openedx_learning/decisions/images/pathway-credentials.dot

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+digraph pathway_credentials {
+    rankdir=LR;
+    fontname="Helvetica";
+    node [shape=box, style=rounded, fontname="Helvetica", fontsize=11];
+    edge [fontname="Helvetica", fontsize=10];
+
+    signal [label="course passing-status\nDjango signal", shape=ellipse];
+    handler [label="re-evaluate Item fulfillment\nfor learner's enrolled Pathways\ncontaining that course"];
+    decide [label="all Items\nfulfilled?", shape=diamond, style=""];
+    issue [label="issue certificate:\nstore self-contained record,\nemit event"];
+    render [label="HTML certificate\n(viewable, printable)"];
+
+    signal -> handler -> decide;
+    decide -> issue [label="yes"];
+    decide -> done [label="no"];
+    done [label="done", shape=plaintext];
+    issue -> render;
+}