v0.97 Expose public key and connection path (relay / direct) via agent

What's Changed

• Define Tailcat live-path agent protocol by @Sniperlyf3 in #45
• Bound fake-agent frame allocations by @Sniperlyf3 in #47
• Expose Tailcat live path status from the active engine by @Sniperlyf3 in #46
• Add truthful Tailcat path reporter primitive by @Sniperlyf3 in #48
• Prove DERP admission enforcement in E2E harness by @Sniperlyf3 in #50
• Expose live Tailcat path status to .NET by @Sniperlyf3 in #51

Full Changelog: v0.96...v0.97