feat(mcp): Add reopen command support for closed issues

Implements the `bd` reopen command across the entire MCP stack, enabling
agents to reopen closed issues with optional reason tracking for audit
trails. This addresses the need to handle regressions and incorrectly
closed issues without manual `bd` CLI intervention.

The reopen command is more explicit than `bd update --status open` and
emits a dedicated Reopened event in the audit log, making it easier to
track why issues were reopened during analysis.

Changes:
  - `models.py`: Add ReopenIssueParams with issue_ids list and optional reason
  - `bd_client.py`: Implement reopen() method with JSON response parsing
  - `tools.py`: Add beads_reopen_issue() wrapper with Annotated types for MCP
  - `server.py`: Register 'reopen' MCP tool with description and parameters

Testing (10 new):
  - `test_bd_client.py`: 4 unit tests (mocked subprocess)
  - `test_bd_client_integration.py`: 3 integration tests (real `bd` CLI)
  - `test_mcp_server_integration.py`: 3 MCP integration tests (FastMCP Client)
  - `test_tools.py`: 3 tools wrapper tests (mocked BdClient)

Also updated `README.md`.

integrations/beads-mcp/tests/test_mcp_server_integration.py

@@ -221,6 +221,96 @@ async def test_close_issue_tool(mcp_client):
     assert closed["closed_at"] is not None
 
 
+@pytest.mark.asyncio
+async def test_reopen_issue_tool(mcp_client):
+    """Test reopen_issue tool."""
+    import json
+
+    # Create and close issue
+    create_result = await mcp_client.call_tool(
+        "create", {"title": "Issue to reopen", "priority": 1, "issue_type": "bug"}
+    )
+    created = json.loads(create_result.content[0].text)
+    issue_id = created["id"]
+
+    await mcp_client.call_tool(
+        "close", {"issue_id": issue_id, "reason": "Done"}
+    )
+
+    # Reopen issue
+    reopen_result = await mcp_client.call_tool(
+        "reopen", {"issue_ids": [issue_id]}
+    )
+
+    reopened_issues = json.loads(reopen_result.content[0].text)
+    assert len(reopened_issues) >= 1
+    reopened = reopened_issues[0]
+    assert reopened["id"] == issue_id
+    assert reopened["status"] == "open"
+    assert reopened["closed_at"] is None
+
+
+@pytest.mark.asyncio
+async def test_reopen_multiple_issues_tool(mcp_client):
+    """Test reopening multiple issues via MCP tool."""
+    import json
+
+    # Create and close two issues
+    issue1_result = await mcp_client.call_tool(
+        "create", {"title": "Issue 1 to reopen", "priority": 1, "issue_type": "task"}
+    )
+    issue1 = json.loads(issue1_result.content[0].text)
+
+    issue2_result = await mcp_client.call_tool(
+        "create", {"title": "Issue 2 to reopen", "priority": 1, "issue_type": "task"}
+    )
+    issue2 = json.loads(issue2_result.content[0].text)
+
+    await mcp_client.call_tool("close", {"issue_id": issue1["id"], "reason": "Done"})
+    await mcp_client.call_tool("close", {"issue_id": issue2["id"], "reason": "Done"})
+
+    # Reopen both issues
+    reopen_result = await mcp_client.call_tool(
+        "reopen", {"issue_ids": [issue1["id"], issue2["id"]]}
+    )
+
+    reopened_issues = json.loads(reopen_result.content[0].text)
+    assert len(reopened_issues) == 2
+    reopened_ids = {issue["id"] for issue in reopened_issues}
+    assert issue1["id"] in reopened_ids
+    assert issue2["id"] in reopened_ids
+    assert all(issue["status"] == "open" for issue in reopened_issues)
+    assert all(issue["closed_at"] is None for issue in reopened_issues)
+
+
+@pytest.mark.asyncio
+async def test_reopen_with_reason_tool(mcp_client):
+    """Test reopening issue with reason parameter via MCP tool."""
+    import json
+
+    # Create and close issue
+    create_result = await mcp_client.call_tool(
+        "create", {"title": "Issue to reopen with reason", "priority": 1, "issue_type": "bug"}
+    )
+    created = json.loads(create_result.content[0].text)
+    issue_id = created["id"]
+
+    await mcp_client.call_tool("close", {"issue_id": issue_id, "reason": "Done"})
+
+    # Reopen with reason
+    reopen_result = await mcp_client.call_tool(
+        "reopen",
+        {"issue_ids": [issue_id], "reason": "Found regression"}
+    )
+
+    reopened_issues = json.loads(reopen_result.content[0].text)
+    assert len(reopened_issues) >= 1
+    reopened = reopened_issues[0]
+    assert reopened["id"] == issue_id
+    assert reopened["status"] == "open"
+    assert reopened["closed_at"] is None
+
+
 @pytest.mark.asyncio
 async def test_ready_work_tool(mcp_client):
     """Test ready_work tool."""