Document Tooltip and DatePickerInput and improve Common and Dialogs landings

[woksin]

Problem

Tooltip and DatePickerInput are public exports from @cratis/components/Common and are classified as interaction primitives, but neither has a navigable reference page. They appear only incidentally in styling, migration, and CommandForm documentation.

The Common and Dialogs landing pages also mostly repeat their toc children rather than helping readers choose between the available primitives.

Proposed scope

• Add Documentation/Common/tooltip.md and Documentation/Common/date-picker-input.md from the current public source, stories, and specs.
• Document props, value contracts, stable parts, and verified interaction behavior without overstating accessibility guarantees.
• Register and link both pages from the Common toc/landing and existing references.
• Rewrite the Common and Dialogs landing pages as concise selection guides instead of duplicated link lists.
• Preserve Common and Dialogs as separate package/documentation boundaries.

Acceptance criteria

• Every public Common interaction primitive has a navigable reference page.
• Tooltip documentation acknowledges the current open content-type contract issue rather than contradicting it.
• DatePickerInput documentation does not claim unresolved segment target-size behavior is complete.
• Common and Dialogs landings explain which component to choose and do not merely repeat their toc.
• Components authoring, Markdown, local-link, and rendered-site checks pass.

Dependencies

• Reflect, but do not absorb, the existing Tooltip content contract and DatePicker target-size issues.

Exclusions

• Do not merge Common and Dialogs sections.
• Do not change source types or component behavior.
• Do not add stories as part of this documentation issue.
• Do not restructure Toolbar tooltip-position documentation.