fix: exit 1 when zero validators accept or have PAT stored

[Tet-9]

Fixes #542

Problem

Both miner post and miner check exit with code 0 even when
accepted_count == 0 or valid_count == 0. This means CI/CD pipelines
treating exit codes as success/failure indicators will incorrectly treat
a failed broadcast as success.

Fix

Added sys.exit(1) after the display block in both commands when the
operation produced zero successful results.

Changes

• gittensor/cli/miner_commands/post.py — exit 1 when accepted_count == 0
• gittensor/cli/miner_commands/check.py — exit 1 when valid_count == 0