Server server-v0.6.6

What's Changed

• Keep the ggml headers under libs/, beside the tag and patches they come from by @thewh1teagle in #1503
• Keep the fetched ggml libraries under libs/lib too, and retire third_party/ by @thewh1teagle in #1504
• Ship the sidecar as vibe-server from this repository's server releases by @thewh1teagle in #1502
• chmod the renamed sidecar, not the old name by @thewh1teagle in #1506
• Docs: the engine is server/, shipped as vibe-server by @thewh1teagle in #1507
• Call the engine server, not sona, throughout the app and handoff by @thewh1teagle in #1508
• Test fixture: the death report says vibe-server now by @thewh1teagle in #1509
• Finish the rename: installer hook, VIBE_SERVER_* environment, and the engine's own prose by @thewh1teagle in #1510
• server docs: server release, not sona release by @thewh1teagle in #1511

Full Changelog: server-v0.6.5...server-v0.6.6