fix(providers): bind multi-route grants to admitted endpoints

[shiju-nv]

Summary

Requests to different provider paths on one host now acquire the grant belonging to an endpoint that admitted that request. The relay checks each request on a persistent connection against current provider state, and rejects a grant if policy or provider installation changes before forwarding. This adds the missing multi-route hook and applies the same ownership checks to existing single-route REST injection.

Related Issue

Closes #3657

The implementation covers #3657's multi-route injection, isolation, persistent connections, failure recovery and refresh/expiry requirements. Native single-route MCP/JSON-RPC remains tracked separately in #3658, as #3657 permits. Native single-route GraphQL also still lacks its injection hook; this PR does not claim to add it. The broader issuer-expiry/TTL correction remains separate.

Changes

• Generate endpoint owner IDs from provider identity and complete policy rules, carry them through policy and credential delivery, and ignore authored owner stamps. Global policies retain their existing replacement semantics.
• Query which individual endpoints admit the request and caller, then filter credentials by those owners before selector ranking. Preserve ordinary union allows and global denies. Audit forwarding cannot borrow a grant from a denying owner.
• Resolve from a fresh provider snapshot on each inspected request. Include installation identity in cache keys and check policy/provider freshness across acquisition and body buffering, including same-revision repair and HTTP/1.0 requests without Host.
• Add gateway, OPA, relay, cache and Podman regressions. Document credential selection and refresh behavior in the provider-profile guide.

Testing

• Checks appropriate to the affected code and behavior pass
• Unit tests added/updated (if applicable)
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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