docs: state the facts without arguing for them

[kannandreams]

Summary

The Security page had picked up a defensive register — sentences spending words insisting on a point the surrounding fact already made:

Was	Now
"That figure is not typed into the page."	(cut; the mechanism sentence that followed already says it)
"a consequence of its design, not a policy bolted on afterward … never needs more trust than any other unprivileged process"	"agent-top is read-only and local-only. It reads the transcripts a harness already wrote and the process table the OS already keeps, and changes neither."
"The network, enumerated exactly" / "Two calls, both narrow enough to name in full"	"Network calls" / "There are two."
"It has nothing to leak on that front because it was never given anything to hold."	(cut)
"the source is the whole story"	(cut)
"The daily schedule is the one that matters most."	"The daily run catches what a push cannot: …"

Same tic removed from the tracing post: "A debugging session, not a demo" → "Debugging a slow turn", plus two asides that announced their own honesty ("worth being honest about", "That's the actual point"). README security section loses "part of the security story" and gains the schedule instead.

No facts changed or dropped.

Test plan

• mise run docs:build (strict) passes.