Guard the telemetry disclosure, and unwind the README's em-dashes

[mattpodwysocki]

Two things, both about the README saying what it means.

A guard, because the disclosure already drifted once

The Privacy section claimed we collect exit codes, which we never have; described the command/ marker as a command name when it's the service; and didn't mention the terminal markers at all, which go out on every request. Prose and code drifted because nothing compared them.

every_telemetry_marker_is_disclosed now does, in the blunt spirit of the other guards in that file. A table pairs each marker with the words in README.md that disclose it, and it fails in both directions:

# disclosure removed from the README
README.md's Privacy section no longer says "stdin and stdout are attached to a
terminal", which is what discloses the `stdin_tty/` marker. Either put it back
or update DISCLOSED.

# marker added to telemetry.rs
telemetry_markers gained or lost a marker. Add a DISCLOSED row and a sentence
in README.md's Privacy section, then update this count.

Both verified by making them happen, rather than trusting a green tick. It doesn't prove the disclosure is well written — only that nothing we send is missing from it, and that the sentence disclosing something can't quietly be edited away.

The prose

Twenty-nine em-dashes, nearly all the same sentence — explanatory clause habit. At that consistency it reads as machine-written, which it largely was. Gone, mostly by ending the sentence or using a colon where a list actually follows.

The densest paragraph got restructured rather than repunctuated. "Fifteen agents are known" now says supported, and the three flags that were buried in the same paragraph as a fifteen-item list are a table, which is how this README presents flags everywhere else:

Flag	What it does
--agent <name>	Install for one agent. Repeatable.
--global	Write to the agent's home directory instead of this project.
--dir <path>	Write to a directory you name, for a Dockerfile or a CI job.

Also unpicked two over-long sentences — the 40-word one about command groups versus spec files, and the 36-word one about signed builds.

One em-dash stays, deliberately

Dry run — nothing was sent. is quoted output, and executor.rs:606 prints it with the dash. I flattened it at first, which made the README misquote the binary, and reverted.

Worth knowing there are four more of those in agent_skills.rs (Dry run — nothing was written/changed/removed). Changing the strings the binary prints is a different decision from editing docs, so I left them; say the word if you want them too.

No fenced block changed at all — verified by diffing the set of code-block lines before and after, so every command and every sample output is byte-identical. Only prose moved.

602 tests, fmt and clippy clean, and no in-page anchor broken.