v0.5: local breach-corpus lookup to auto-fill breached_passwords

[StreamDemon]

Idea

Auto-populate breached_passwords (the highest-yield stream, currently hand-entered)
by looking the subject up in a local HIBP / combo corpus.

Design considerations (needs its own pass)

• Corpus format and lookup key (email / handle).
• This is the most privacy-sensitive operation in the tool. Local-only, no network
  lookups against a live service. Document the authorized-use posture.
• Never commit any corpus or any real result.

Acceptance criteria

• Local lookup that fills breached_passwords from a user-supplied local corpus
• No network calls; corpus stays local and gitignored
• Ethics / authorization note in docs
• selftest coverage (synthetic corpus)
• CHANGELOG updated