chore: add bounded contributor agreement

[fazpu]

Summary

• add the RememberStack CLA v1.0 with an irrevocable inbound grant and an independently enforceable self-hosting covenant
• add a narrow trademark policy and focused contribution guidance
• add the versioned pull-request assent template and metadata-only CLA workflow
• record D77 naming-risk acceptance and keep status honest that branch-protection activation follows merge

This is bootstrap PR 1 of 2. After merge, the CLA status will be made required with administrator enforcement; activation PR 2 will pin the agreement link to this merge commit, prove the required check, and close the remaining status items.

Verification

• CLA workflow exact checked/unchecked/bot cases exercised locally
• workflow YAML parsed successfully
• website typecheck and production build passed
• release contract passed for v0.1.0
• Grok 4.5 adversarial re-review: BLOCKERS: NONE

Contributor agreement

Signing on behalf of a legal entity (leave blank if accepting individually): WriteIt.ai s.r.o.

• I have read and agree to the RememberStack Contributor License Agreement v1.0.

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.