fix: healthchecks and add standard port sync server access

[cfsmp3]

Summary

• Fix Docker healthchecks to use wget instead of curl (curl is not available in Alpine-based containers)
• Use 127.0.0.1 instead of localhost in healthchecks (localhost doesn't resolve correctly in some Alpine containers)
• Fix syncserver healthcheck to check / instead of /health (taskchampion-sync-server doesn't have a /health endpoint)
• Add /taskchampion/ path in nginx config for sync server access on standard port 443
• Update example.frontend.env to use the new /taskchampion/ path as default

Changes

1. docker-compose.yml: Fixed all three healthchecks
2. production/example.nginx.conf: Added /taskchampion/ location block, marked port 8080 as legacy
3. production/example.frontend.env: Updated to use /taskchampion/ path with legacy option documented

Benefits

• Healthchecks now work correctly (containers show "healthy" instead of "unhealthy")
• Users can access sync server on standard HTTPS port 443 via /taskchampion/ path
• No need to open additional firewall port (8080) in production
• Legacy port 8080 still supported for backward compatibility

Test plan

• Run docker compose up -d and verify all containers show healthy status
• Verify sync server accessible at /taskchampion/ path
• Verify legacy port 8080 still works

🤖 Generated with Claude Code

[github-actions]

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[its-me-abhishek]

this works fine with the Setup Guide, backend env need not be updated, as Docker connects internally anyways.