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.

app/code_links.py

@@ -0,0 +1,106 @@
+"""Code links (roadmap #1): what code belongs to a card?
+
+Pure matching helpers — a branch, pull request or commit is linked
+to an issue when it references the issue number the way developers
+actually write it: `#12` in a title/body/message, or the number as
+a token in a branch name (`feature/12-login`, `issue-12`, `12-fix`).
+"""
+
+import re
+
+_REF_RE = re.compile(r"(?<![\w#])#(\d+)\b")
+_BRANCH_TOKEN_RE = re.compile(r"(?:^|[-_/])(\d+)(?:[-_/]|$)")
+
+
+def extract_issue_refs(text: str | None) -> set[int]:
+    """All #n references in a text (titles, bodies, messages)."""
+    if not text:
+        return set()
+    return {int(m.group(1)) for m in _REF_RE.finditer(text)}
+
+
+def branch_issue_number(branch_name: str | None) -> int | None:
+    """The issue number encoded in a branch name, if any."""
+    if not branch_name:
+        return None
+    m = _BRANCH_TOKEN_RE.search(branch_name)
+    return int(m.group(1)) if m else None
+
+
+def find_code_links(
+    branches: list[dict],
+    pulls: list[dict],
+    commits: list[dict],
+    number: int,
+) -> dict:
+    """Linked branches/PRs/commits for one issue number."""
+    linked_branches = [
+        b.get("name", "")
+        for b in branches
+        if branch_issue_number(b.get("name")) == number
+    ]
+    linked_pulls = []
+    for pr in pulls:
+        head_ref = ((pr.get("head") or {}).get("ref")) or ""
+        refs = extract_issue_refs(pr.get("title")) | extract_issue_refs(
+            pr.get("body")
+        )
+        if number in refs or branch_issue_number(head_ref) == number:
+            linked_pulls.append(
+                {
+                    "number": pr.get("number"),
+                    "title": pr.get("title", ""),
+                    "state": pr.get("state", "open"),
+                    "merged": bool(pr.get("merged")),
+                    "html_url": pr.get("html_url", ""),
+                    "branch": head_ref,
+                }
+            )
+    linked_commits = []
+    for commit in commits:
+        message = ((commit.get("commit") or {}).get("message")) or ""
+        if number in extract_issue_refs(message):
+            linked_commits.append(
+                {
+                    "sha": (commit.get("sha") or "")[:7],
+                    "message": message.splitlines()[0] if message else "",
+                    "html_url": commit.get("html_url", ""),
+                    "date": (
+                        ((commit.get("commit") or {}).get("author") or {}).get(
+                            "date", ""
+                        )
+                        or ""
+                    )[:10],
+                }
+            )
+    # Best PR to badge: a merged one beats an open one beats closed.
+    pr_badge = None
+    for wanted in ("merged", "open", "closed"):
+        for pr in linked_pulls:
+            state = (
+                "merged" if pr["merged"]
+                else "open" if pr["state"] == "open" else "closed"
+            )
+            if state == wanted:
+                pr_badge = {
+                    "number": pr["number"],
+                    "state": state,
+                    "label": {
+                        "merged": "fusionnée",
+                        "open": "ouverte",
+                        "closed": "fermée",
+                    }[state],
+                }
+                break
+        if pr_badge:
+            break
+    return {
+        "branches": linked_branches,
+        "pulls": linked_pulls,
+        "commits": linked_commits,
+        "summary": {
+            "branches": len(linked_branches),
+            "commits": len(linked_commits),
+            "pr": pr_badge,
+        },
+    }