Rename MCP server identifier from state-hub to dev-hub

Introduce canonical MCP_SERVER_NAME constants, shared registration helpers,
and a migrate_mcp_config.py script for ~/.claude.json upgrades. Registration,
patch, and custodian CLI checks accept both dev-hub and legacy state-hub during
transition. API root metadata and session-protocol template reflect the new name.

mcp_server/server.py

@@ -19,10 +19,12 @@ import httpx
 from fastmcp import FastMCP
 from hub_core.mcp import HubCoreMCPServer
 
+from mcp_server.constants import MCP_SERVER_NAME
+
 API_BASE = os.environ.get("API_BASE", "http://127.0.0.1:8000").rstrip("/")
 
 mcp = FastMCP(
-    name="state-hub",
+    name=MCP_SERVER_NAME,
     instructions=(
         "Custodian State Hub: tracks topics, workstreams, tasks, decisions, and progress events. "
         "Start every session with get_state_summary() for orientation. "
@@ -45,7 +47,7 @@ _HUB_CORE_MCP_EXCLUDE = frozenset({
     "ingest_tpsc_tool",
 })
 HubCoreMCPServer(
-    name="state-hub",
+    name=MCP_SERVER_NAME,
     api_base=API_BASE,
     register_tools=False,
 ).attach_to(mcp, exclude=_HUB_CORE_MCP_EXCLUDE)