docs: clarify AVE-2026-00073 scope (MCP server URL, agent_card_url)

[chaksaray]

Summary

• Scope-clarification only, no new record, no score change (aivss_score stays 4.1 MEDIUM).
• While verifying a candidate flagged from predictor2718's cfgaudit PR crosswalks: refresh cfgaudit to v1.11.0 (53 rules onto 23 classes) #123 (a committed cleartext http:// endpoint for an MCP server URL or agent_card_url), it turned out AVE-2026-00073 already covers this -- its detection_methodology step 3 and remediation already say to reject cleartext http:// destinations "regardless of whether the host itself is otherwise legitimate." See discussion on crosswalks: refresh cfgaudit to v1.11.0 (53 rules onto 23 classes) #123.
• The only real gap was textual: payload_surface and behavioral_fingerprint named a model/provider base URL and telemetry endpoint explicitly, but left MCP server URLs and agent_card_url under an implicit "an equivalent traffic-destination value" catch-all.
• Updated description, behavioral_fingerprint, provenance_vector.payload_surface, example_patterns (two new examples: an mcpServers[].url and an agent_card_url, both cleartext), and detection_methodology to name both explicitly. Added a dated note to aivss.notes documenting why, per the "frozen files are never edited retroactively, but active records track changes via last_updated" convention. last_updated bumped to today; published unchanged.
• CHANGELOG.md gets a ### Changed entry, not ### Added, since no ave_id was created.

Test plan

• python3 scripts/validate_records.py -- 75/75 records valid
• python3 scripts/check_fixtures.py
• pytest tests/ -x -q -- 301 passed
• node scripts/build-records.js -- dist regenerated, frozen v1.1.0 snapshot untouched
• README record count untouched (no new record, count still 75 as of this branch's base)