docs(pods): refocus on distributed/sharded inference

Strip Thor backend features (Drive, VM, services, connectors, domains,
templates, federation, capsule, budgets). Page now covers: install,
what pods are, quick start (create→invite→join→shard→query), layer
sharding internals (3 libp2p protocols + inference flow), smart routing
(4-tier priority), model recommendations by combined VRAM, API keys
(Python + TS + curl), full command reference, and Claude Code MCP setup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Varun