fix: harden Anthropic proxy shape guard

[ppiankov]

Summary\n- fail closed on unsupported methods and malformed request shapes while preserving valid Anthropic-compatible gateway paths\n- treat model identity as advisory so any provider speaking the Anthropic wire shape remains supported\n- route request mutation through one evidence-aware gateway: exact provider formats, known values, and operator rules authorize replacement\n- scan contract fields without rewriting uncertain built-in matches; scan tool input examples and stop sequences under the same policy\n- detect standalone provider tokens and contain complete structured secrets without overcapturing adjacent content\n- tighten legacy Vault token grammar so code-like dotted identifiers are never mutated\n- fail closed on malformed private-key containers, invalid routed-proxy custom rules, and request-body serialization failures\n- let non-routed agents launch without validating proxy rules they do not consume\n- harden launch loopback cleanup, termination handling, refusal accounting, and disconnect logging\n- document evidence-based mutation scope and one-way proxy versus reversible MCP behavior\n\n## Work orders\nImplemented: WO-275, WO-410, WO-419, WO-422-WO-430, WO-436-WO-458, WO-461-WO-463, WO-465-WO-470, WO-472, WO-473, WO-478-WO-488, WO-491, WO-494, WO-495.\n\nReviewed and rejected as invalid or already covered: WO-489, WO-490, WO-492, WO-493, WO-496, WO-497, WO-498.\n\n## Verification\n- 954 Swift tests pass locally\n- mutation authorization, provider-pattern, containment, shape-guard, launch, and real-TCP regressions pass\n- debug build passes\n- SwiftLint strict reports 0 violations\n- GitHub CI is running on the current head\n