docs(lstk): update CLI reference to v0.15.0

Bring the lstk CLI reference up to date with the current CLI surface
(last documented around v0.12/v0.13, now v0.15.0):

- Document the CLI/IaC proxy tools: az (+ start/stop-interception),
  terraform (tf), cdk, sam.
- Add setup azure; correct setup aws (now has --force and a
  non-interactive mode, no longer interactive-only).
- Add snapshot show and S3-remote support for snapshot save/load/list
  (--profile, credential precedence, running-emulator requirement).
- Note snapshot now works for Snowflake/Azure with an experimental
  warning; only reset stays AWS-only.
- Add global --snapshot/--no-snapshot flags and snapshot auto-load on
  start; document LOCALSTACK_ env forwarding.
- Add config fields image, volumes, and snapshot; add a Volume mounts
  section.
- Add an Extensions section.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QRmA1n8vtvoT3DnGQzRk87

Author: gtsiolis