Redact credentials from upstream proxy success messages

[MatousMarik]

Problem

Two tools echo the upstream proxy URL back verbatim:

// src/tools/upstream.ts:25
message: `Global upstream set to ${proxy_url}`,
// src/tools/upstream.ts:71
message: `Upstream for '${hostname}' set to ${proxy_url}`,

Upstream URLs routinely carry credentials — both tool descriptions advertise
socks5://user:pass@host:port. MCP tool results are persisted in the client
transcript, so each call writes the upstream password into the conversation log
a second time, on top of the call arguments.

proxy_mobile_setup also accepts upstream_proxy_url but reports only
upstream_set: <boolean>, so it is already fine.

Acceptance criteria

• Both success messages redact the password while keeping scheme, username,
  host, port and path visible:
  Global upstream set to http://groups-RESIDENTIAL,country-US:***@proxy.apify.com:8000
• The username is deliberately preserved. For several providers the username
  field is configuration rather than a secret — with Apify Proxy it encodes
  proxy group, country and sticky-session id — and it is what makes the
  confirmation message worth printing. Only the password is replaced.
• A URL with no password is unchanged.
• A URL that fails to parse is reported as <unparseable url> or similar, never
  echoed verbatim as a fallback.
• Redaction lives in a pure exported function in src/utils.ts, covered in
  test/unit/utils.test.ts, with cases for: user+password, username only,
  no userinfo, empty password (user:@host), percent-encoded credentials,
  a socks5:// URL, a pac+http:// URL, and an unparseable string.
• Add no runtime dependency. new URL() handles every scheme in use here,
  including socks5://, pac+http://, and usernames containing commas.

Verification

npm run build && npm run test:unit