feat: proxy port from config + config set/init commands

[zx06]

Summary

Feature 1: Proxy Port from Config

• Add local_port field to Profile config for proxy port persistence
• When config local_port is set and port is in use:
  • TTY: prompt user to choose random port or quit
  • Non-TTY: return XSQL_PORT_IN_USE error
• Port priority: --local-port flag > profile.local_port > 0 (auto)

Feature 2: Config Set/Init Commands

• xsql config init - create template config file
• xsql config set <key> <value> - quick config modification
  • Supports profile.<name>.<field> and ssh_proxy.<name>.<field>

Changes

• internal/config/types.go: Add LocalPort to Profile
• internal/config/write.go: Config write/update capability
• internal/proxy/proxy.go: Port conflict detection with XSQL_PORT_IN_USE
• cmd/xsql/proxy.go: Config-based port resolution + TTY conflict prompt
• cmd/xsql/config.go: New config init/set commands
• internal/errors/codes.go: New XSQL_PORT_IN_USE error code
• RFC 0006 + updated docs (cli-spec, config, error-contract)
• Comprehensive unit tests and E2E tests

Testing

• All existing tests pass
• New unit test coverage: config write (89%), proxy (94%), errors (87%)
• E2E tests for config init, config set, proxy port from config

[codecov]

Codecov Report

❌ Patch coverage is 79.15058% with 54 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.92%. Comparing base (2a58171) to head (5a983b4).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cmd/xsql/proxy.go	20.58%	26 Missing and 1 partial ⚠️
internal/config/write.go	86.00%	14 Missing and 7 partials ⚠️
cmd/xsql/config.go	86.95%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
- Coverage   82.03%   80.92%   -1.11%     
==========================================
  Files          37       40       +3     
  Lines        2449     2726     +277     
==========================================
+ Hits         2009     2206     +197     
- Misses        331      397      +66     
- Partials      109      123      +14     

Flag	Coverage Δ
e2e	44.09% <0.00%> (-0.22%)	⬇️
integration	44.09% <0.00%> (-0.22%)	⬇️
unittests	68.23% <79.15%> (+0.32%)	⬆️

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[sonarqubecloud]

Quality Gate failed

Failed conditions
21.3% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud