Close IPv6 and JSON-key gaps in IP redaction

Review found addresses the ip category left visible and one way it broke a custom rule:

• A custom pattern named "ip" inherited the built-in context checks, so the documented full-coverage workaround stopped matching bare addresses. The checks now apply to the built-in regexes only.
• Bracketed endpoints ([fd00::5]:8080), an address after a separator colon (host:fe80::1), eight-colon compressed forms, and all-letter private addresses (fdab::abcd) are redacted; a[1::2] and c::d are not.
• JSONL values are scanned without their key, so {"host":"203.0.113.9"} had no context. A key naming an address now counts as context.