SOMNUS.md spec drift: absolute "cannot autonomously create" claim was only true of one subsystem

docs/SOMNUS.md's headline claim, "Somnus cannot autonomously create or remove anything in the graph," reads as an absolute statement about the whole nightly Somnus pipeline. Investigating packages/graph/src/gds/ and packages/graph/src/gds/somnus/ showed the claim was only ever true of the dreamSomnus LLM reasoning loop (validate/weaken apply directly, propose/reject/abstract go through an agent-evaluation pool). It was never true of the surrounding nightly pipeline, which the doc didn't distinguish from the reasoning loop.