feat(doctor): Add doctor command

[tab]

• Check configuration, environment, services, topology, and runtime without starting services
• Support --summary and --json output, with exit codes 0/2/3 for scripting and CI
• Extract config.LoadPath, deduping the cmd config-loading wrapper

[sentry]

Codecov Report

❌ Patch coverage is 87.98989% with 95 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.62%. Comparing base (6fdafe0) to head (dd1b3d7).

Files with missing lines	Patch %	Lines
internal/app/doctor/runtime.go	53.95%	62 Missing and 2 partials ⚠️
internal/app/doctor/environment.go	81.48%	8 Missing and 2 partials ⚠️
cmd/main.go	0.00%	6 Missing ⚠️
internal/app/doctor/services.go	96.22%	3 Missing and 3 partials ⚠️
internal/app/doctor/render.go	95.91%	3 Missing and 1 partial ⚠️
internal/app/cli/cli.go	80.00%	2 Missing and 1 partial ⚠️
internal/app/cli/commands.go	93.75%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #144      +/-   ##
==========================================
- Coverage   89.66%   89.62%   -0.05%     
==========================================
  Files          66       76      +10     
  Lines        6658     7438     +780     
==========================================
+ Hits         5970     6666     +696     
- Misses        532      609      +77     
- Partials      156      163       +7     

Files with missing lines	Coverage Δ
internal/app/doctor/checks.go	100.00% <100.00%> (ø)
internal/app/doctor/config.go	100.00% <100.00%> (ø)
internal/app/doctor/doctor.go	100.00% <100.00%> (ø)
internal/app/doctor/runner.go	100.00% <100.00%> (ø)
internal/app/doctor/topology.go	100.00% <100.00%> (ø)
internal/config/loader.go	84.61% <ø> (ø)
internal/config/resolve.go	100.00% <100.00%> (ø)
internal/app/cli/commands.go	93.82% <93.75%> (-0.02%)	⬇️
internal/app/cli/cli.go	81.96% <80.00%> (-0.65%)	⬇️
internal/app/doctor/render.go	95.91% <95.91%> (ø)
... and 4 more

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

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