fix: bind SSE to 0.0.0.0 in Docker for port mapping

[alexei-led]

Summary

• Auto-detect Docker environment using /.dockerenv and /proc/self/cgroup
• Bind SSE server to 0.0.0.0 in Docker (required for port mapping)
• Bind SSE server to 127.0.0.1 on host (secure localhost-only)

Problem

When running the MCP server in Docker with SSE transport, the server bound to 127.0.0.1:8000 inside the container. This made it inaccessible from the host even with port mapping (-p 8001:8000).

Solution

Smart host binding based on environment detection:

Environment	Host Binding	Rationale
Docker	0.0.0.0	Required for port mapping to work
Host (uvx)	127.0.0.1	Secure, localhost-only access

Security Considerations

• Host (uvx with sandbox): Binds to localhost only - prevents accidental network exposure
• Docker: Binds to all interfaces but Docker's network namespace provides isolation; users can further restrict via -p 127.0.0.1:8000:8000

Test plan

• uvx SSE binds to 127.0.0.1:8000
• Docker SSE binds to 0.0.0.0:8000
• Docker SSE accessible from host via port mapping
• All 218 unit tests pass
• Lint/format checks pass

[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.40%. Comparing base (c8db24c) to head (d7bae4d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/aws_mcp_server/config.py	11.11%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #27      +/-   ##
==========================================
- Coverage   91.29%   90.40%   -0.89%     
==========================================
  Files           8        8              
  Lines         804      813       +9     
==========================================
+ Hits          734      735       +1     
- Misses         70       78       +8     

Files with missing lines	Coverage Δ
src/aws_mcp_server/config.py	60.00% <11.11%> (-40.00%)	⬇️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.