fix: describe Trust Gate egress metadata as selected fields, not redacted

[yia-mw-agent]

What

Repair of a confirmed diagnostic/docs defect found during issue #125 installed-runtime acceptance on merged cefc7bd: the Trust Gate data-egress disclosure (doctor, MCP startup notice, and trust_gate_egress on tool responses) described the transmitted metadata as "selected redacted metadata".

That contradicts the actual behavior and the operator's explicit correction for #123/#125: FAVA sends the full scope-resolved Trust Gate prompt, the full candidate thought body, and the complete selected metadata fields; agent_id and metadata.extra are excluded — nothing sent is redacted.

Changes

• src/fava_trails/trust_gate.py: reword both llm-oneshot and decisions data_sent_summary text to "selected metadata fields" and state that agent_id and metadata.extra are excluded and never sent; align llm-oneshot data_sent lines with the decisions policy style; correct the _redact_metadata docstring (field selection, not value redaction).
• Docs aligned: AGENTS_SETUP_INSTRUCTIONS.md, docs/fava_trails_faq.md, docs/secret-preflight.md, docs/fava_trails_onepager.html, src/fava_trails/integrations/codev/README.md.
• Regression coverage: updated existing disclosure assertions and added test_describe_metadata_disclosure_never_says_redacted_for_either_policy — no disclosure (either policy) may describe transmitted metadata as "redacted", and the exclusions must be stated explicitly.
• CHANGELOG entry under Unreleased / Fixed.

Verification

• uv run pytest tests/test_trust_gate_egress.py tests/test_trust_gate.py tests/test_trust_gate_decisions.py — 108 passed
• uv run pytest (full suite) — 1095 passed; 5 tests/test_jj_backend.py failures observed only in the full run and pass in isolation (pre-existing ordering flake, unrelated to this change)
• uv run ruff check on all touched files — clean

Acceptance context (issue #125, supplied by Captain)

Installed-runtime acceptance on cefc7bd (this wording defect confirmed there):

• Jev approved a quality memory at Noul probability 0.90 with threshold 0.5
• Jev rejected a vague memory at probability 0.04
• Server restart preserved the approved record and Decisions provenance
• Invalid credential produced a sanitized HTTP 401 fail-closed result with no governed promotion; restored credential returned a valid probability

Closes #125

[timeleft--]

Captain review of exact head acac695: clean. The disclosure now accurately states that the full prompt, full candidate body, and complete selected metadata fields are transmitted, while agent_id and metadata.extra are excluded. Local exact-head validation: ruff passed; 108 affected trust-gate tests passed. The observed 0.45.1 CI failure occurred before tests because GitHub rate-limited the JJ release lookup (HTTP 403), not because of this patch.