[Tanzeel0Hussain]

InterPals no longer serves the old "The requested user does not exist or is
inactive" text for missing users, so the message check never matched and
every username was reported as claimed (false positive).

Missing users now get HTTP 404 with a page that says "User not found".
Existing profiles (e.g. blue) return 200 and do not contain that text.

Changes:

• errorMsg: "The requested user does not exist or is inactive" -> "User not found"

Validation (run locally):

• pytest -m validate_targets_fp --chunked-sites "interpals": passed
• pytest -m validate_targets_fn --chunked-sites "interpals": passed
• pytest (default suite): passed
• CLI check with --local: claimed user found, random user not found

[Tanzeel0Hussain]

Heads-up: #3080 also fixes interpals (via status_code 404 instead of a new
errorMsg). Either approach works; I verified that missing users return 404
with a page containing "User not found", while real profiles do not. Happy
to close this PR in favor of #3080 if maintainers prefer that one.