feat(code): cartes liées au code — branches, PRs, commits (issue #1)

app/code_links.py: appariement pur (#n dans titres/corps/messages,
numéro en jeton de branche). Client: list_branches/list_pulls/
list_commits. Badge sur les cartes (board + fragments live),
section Code lié du panneau détail, /api/issues/{o}/{r}/{n}/code.

tests/conftest.py

@@ -223,6 +223,49 @@ class FakeGitea:
         for label in removed:
             self.label_ops.append(("remove", number, label["name"]))
 
+    async def list_branches(self, owner, repo):
+        return [
+            {"name": "main"},
+            {"name": "feature/1-tache-un"},
+            {"name": "issue-5-focus"},
+        ]
+
+    async def list_pulls(self, owner, repo, state="all"):
+        return [
+            {
+                "number": 16, "title": "Corrige la tâche un",
+                "body": "Fixes #1", "state": "open", "merged": False,
+                "html_url": "http://gitea.test/pr/16",
+                "head": {"ref": "feature/1-tache-un"},
+            },
+            {
+                "number": 17, "title": "Focus", "body": "",
+                "state": "closed", "merged": True,
+                "html_url": "http://gitea.test/pr/17",
+                "head": {"ref": "issue-5-focus"},
+            },
+        ]
+
+    async def list_commits(self, owner, repo, limit=75):
+        return [
+            {
+                "sha": "abcdef1234567890",
+                "html_url": "http://gitea.test/c/abcdef1",
+                "commit": {
+                    "message": "Début de la tâche #1\n\nDétails",
+                    "author": {"date": "2026-10-10T10:00:00Z"},
+                },
+            },
+            {
+                "sha": "1234567abcdef",
+                "html_url": "http://gitea.test/c/1234567",
+                "commit": {
+                    "message": "Commit sans rapport",
+                    "author": {"date": "2026-10-09T10:00:00Z"},
+                },
+            },
+        ]
+
     async def get_milestones(self, owner, repo, state="open"):
         return [
             {