docs: describe request inspection, and correct a limitation that stopped being true

[CharmingGroot]

README said pasu does no L7 content inspection. It does now.

A limitations list that understates what a security tool inspects misleads as badly as one that overstates it — a reader deciding whether pasu covers their case would decide wrongly in both directions.

That entry is now split into what is actually true:

• the kernel layer is L3/L4 and cannot see inside TLS
• the proxy layer inspects content, but only in request shapes it parses
• detection is regex and checksums — no NER, so PII without a pattern (a person's name) is not caught
• it blocks rather than masks

What had no documentation at all

The Inspector plugin point, pasu-pii-kr becoming reachable, and pasu-inspect-presidio appeared in no README, no docs page, and no changelog entry. ## [Unreleased] was empty.

Both READMEs now carry a request-inspection section with the commands, why the request body is the only place content is readable, and what does not survive a Presidio import. The changelog carries a Known gaps heading, not only the additions.

Running the commands caught something

Every command in the new section was run against the built binary rather than written from memory. On a rule file it refuses, the error told the operator to call read_lossy — a library function a person holding a CLI cannot call.

The library no longer names a remedy. Its two callers have different moves available: one can call read_lossy, the other can only change a flag or the file, and naming either is advice the other cannot take. Each now adds its own:

Error: import presidio rules /tmp/rec.yaml

Either remove those recognizers from the file, or lower --presidio-min-score
(currently 0.5) if you accept that a weaker pattern will match more ordinary text.

Caused by:
    1 recognizer(s) could not be imported, so this rule set is not what the file describes:
      Zip code Recognizer — its best pattern scores 0.01, below the 0.5 threshold; …

And the documented workaround does what the docs say it does:

$ pasu-proxy … --presidio-rules ./recognizers.yaml --presidio-min-score 0.0
pasu-proxy: 2 presidio pattern(s) loaded
pasu-proxy: requests are inspected by presidio and refused on a match (rule ids are logged, never the matched text)
pasu-proxy listening on 127.0.0.1:8788

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