guides: genericize the operator name in SEAT-IDENTITY provisioning

Pipeline 2514 failed the sanitization gate on 'Jason mints the token into the
seat slot'. The denylist is jarvis|jason|woltje|... and a shipped framework file
must not carry operator identity. My mistake: I generalized the estate paths and
seat names when promoting this guide and did not check the operator name.

Now reads 'the estate operator', with the accompanying rule that an agent does
not ask another agent to mint one either.

Verified by running tools/quality/scripts/verify-sanitized.sh locally rather than
guessing at the pattern: gate passes.

packages/mosaic/framework/guides/SEAT-IDENTITY.md

@@ -95,7 +95,8 @@ is not how a system finds a credential; the helper resolving the right store is.
 
 1. Create `~/.mosaic/fleet/agents/<seat>/secrets/` mode 700.
 2. Write `.principal` (the Gitea login) and `.scopes` (the granted scopes), mode 600.
-3. Jason mints the token into the seat slot, mode 600. Agents do not mint their own.
+3. The estate operator mints the token into the seat slot, mode 600. Agents do not mint their
+   own, and do not ask another agent to mint one for them.
 4. Symlink the framework store entry to the seat slot.
 5. Verify with an authenticated `GET /user` and confirm the returned login is the seat, **not the
    minting account**. Record the date in `ENTITY.md`. Never record the value.