docs: implement PLAN_NEXT wave 2 docs and governance

[RyshMan]

Problem

Wave 2 of product/PLAN_NEXT.md (docs/DX/OSS/governance consistency) was not implemented on main.

Changes

• Implemented stories 2.1-2.4 and 3.1-3.5 end-to-end.
• Added minimal-dependency install path and release smoke alignment.
• Added canonical state lifecycle docs and linked command/quickstart surfaces.
• Added explicit wrkr fix side-effect contract across CLI help, docs, and README.
• Expanded contributor workflow and Go-only path guidance.
• Added issue templates and PR template with contract/test prompts.
• Added community health baseline files (CODE_OF_CONDUCT.md, CHANGELOG.md).
• Added governance visibility policy docs for product/ and .agents/skills/.
• Added README contract standardization docs and cross-repo follow-up tracker.
• Added hygiene tests for Wave 2 docs/governance contracts.

Validation

• make prepush-full
• ./.tmp/wrkr scan --path ./scenarios/wrkr/scan-mixed-org/repos --state ./.tmp/ship-scan-state.json --json
• go test ./testinfra/hygiene -run 'TestInstallDocsSmokeGoOnlyPath|TestDocsLifecyclePathConsistency|TestDocsSourceOfTruthSectionsPresent|TestContributingContainsRequiredWorkflowSections|TestCommunityTemplatesPresentAndStructured|TestCommunityHealthFilesAndLinks|TestGovernancePolicyDocsPresent|TestReadmeContractSectionsPresent' -count=1
• go test ./core/cli -run TestFixHelpMatchesBehaviorContract -count=1

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