anchor-machine doc: two table rows miss Send-refusal and linked-machine cases #47

Minor from the correctness r2 lens on #25: #25 (comment)

docs/fork/anchor-machine.md lines 31 and 35: two rows of the "what happens when" table describe fewer cases than the
code handles. Send also refuses when the preferred machine cannot use the chosen provider (not installed, not signed
in) or has no recent CPU/memory reading; and a referenced thread on a machine linked to the draft's machine does not
block Send. Fix: add these cases to the two rows (cite the router/Send guard code).

Optional wording nits from the same comment: line 45 example ("connection drops while it opens") may end with Send
refusing instead; line 18: projectless threads start on the primary machine whenever it has a "No project" folder.