feat(docker): add hostname and dns to container create

[retr0h]

Summary

• Add hostname and dns optional fields to DockerCreateRequest for setting container hostname and custom DNS servers at creation time
• Fields flow through all layers: OpenAPI spec → API handler → job payload → agent processor → Docker provider → Docker API
• Validation via spec tags: hostname max 253 chars, dns validates each entry as IP address
• Full test coverage across provider, handler, agent processor, and SDK

Coverage (no regression)

Package	Before	After
controller/api/node/docker	99.6%	99.6%
provider/container/docker	100%	100%
SDK docker methods	100%	100%

Test plan

• Provider tests: hostname only, DNS only, both combined
• Handler unit test: fields propagate to job payload
• HTTP validation: hostname > 253 chars → 400, invalid DNS IP → 400
• Agent processor: hostname+DNS flow through job data
• SDK: create opts with hostname and DNS
• Build clean, lint clean

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main     #347   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files         441      441           
  Lines       21496    21510   +14     
=======================================
+ Hits        21477    21491   +14     
  Misses         11       11           
  Partials        8        8           

Files with missing lines	Coverage Δ
internal/agent/processor_docker.go	100.00% <100.00%> (ø)
...nal/controller/api/node/docker/container_create.go	100.00% <100.00%> (ø)
internal/provider/container/docker/docker.go	100.00% <100.00%> (ø)
pkg/sdk/client/docker.go	100.00% <100.00%> (ø)
pkg/sdk/client/docker_types.go	100.00% <ø> (ø)

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