Spec: Add ClickToSign to component specification

[mikewolfd]

Motivation

The component spec (Section 6, built-in catalog) needs a ClickToSign Progressive component definition. This is the normative foundation that all other slices depend on.

Scope

• Add Section 6.9 (or appropriate number) for ClickToSign in specs/component/component-spec.md
• Define component as: Category Input, Level Progressive, Accepts children No, Bind Required (binds to a group key)
• Compatible pattern: group with accepted (boolean), signedBy (string), signedAt (dateTime), statement (string) children
• Define props: statement (string), buttonLabel (string, default "Sign"), showTimestamp (boolean), showSignerName (boolean), requireTypedName (boolean), revocable (boolean)
• Define rendering requirements (MUST display statement, MUST capture structured attestation on click, MUST propagate required/readonly/relevant)
• Define fallback: Stack containing Text (statement), Toggle (accepted), readonly TextInputs for signedBy/signedAt
• Add to Appendix A component catalog table
• Add to Appendix B compatibility matrix (compatible with group items that follow the attestation children pattern)
• Add "clickToSign" as a valid widgetHint for group items in Section 4.2.5.1 of the core spec
• Run npm run docs:generate and npm run docs:check

Acceptance Criteria

• ClickToSign component fully defined in the component spec with props, rendering requirements, and fallback behavior
• Fallback substitution rule documented in the Progressive fallback table
• "clickToSign" listed as a valid widgetHint for groups in the core spec
• All generated artifacts (*.llm.md, BLUF injections) regenerated and passing checks

Dependencies

None — this is the first slice.