feat: integrate basic-memory MCP for dual memory system

Add basic-memory as a global cross-project knowledge store alongside
the existing per-project .memory/ system. Agents can now persist
reusable patterns, conventions, and lessons learned across all projects
via MCP tools (write_note, search_notes, build_context).

Changes:
- opencode.jsonc: add basic-memory MCP server config
- AGENTS.md: rewrite Project Memory section for dual system with
  routing table (global vs per-project)
- agents/lead.md: integrate basic-memory into phase transitions,
  CONSULT, PHASE-WRAP, escalation, and knowledge freshness
- agents/sme.md: dual caching strategy (basic-memory for cross-project
  guidance, .memory/ for project-specific)

.config/opencode/opencode.jsonc

@@ -38,6 +38,15 @@
 				"chromium"
 			],
 			"enabled": true
+		},
+		"basic-memory": {
+			"type": "local",
+			"command": [
+				"uvx",
+				"basic-memory",
+				"mcp"
+			],
+			"enabled": true
 		}
 	}
 }