docs: establish consumer-driven component governance

[jaavid]

Summary

• adds the component-request issue form
• defines the Proposed → Experimental → Candidate → Stable → Deprecated lifecycle
• adds promotion gates and ownership layers
• records AgentReady consumer evidence
• adds the current component maturity matrix
• records rejected and deferred component decisions
• connects governance to README, Storybook introduction and contribution guidance

Validation

• all eight changed files were fetched successfully from commit fbd5dc26b6ec7606b1ad491637dc4516830f88cd
• runtime exports and package dependencies are unchanged
• AgentReady domain compositions remain outside the shared stable package

Closes #11

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