README: refresh the status paragraph for the Phase 1 close

[EvanWinget]

What changed

One paragraph in the root README. The status text still described Phase 1 as in progress with three operator families implemented. Phase 1 closed on 2026-07-29, so the paragraph now records the close, the complete v0 operator table, the clean oracle diff, and Phase 2 as the next unit of work.

Authority

Not a spec change. The claims restate the Phase 1 done marker in docs/execution-plan.md and the status line at the top of spec/VM.md.

How to review

1. Read the single commit's diff against README.md.
2. Cross-check the claims: docs/execution-plan.md (Phase 1 "Done 2026-07-29" block) and spec/VM.md line 3.
3. Independent verification of the "pinned by vectors, zero unexplained divergence" claims:

   .venv/bin/pytest python/tests
   .venv/bin/python tools/run_vectors.py
   .venv/bin/python tools/diff_clvm.py --count 10000 --seed 20260730