[feat]: Update `<pf-v6-timestamp>` for PatternFly v6

Summary

Update `` to implement the PatternFly v6 Timestamp component.

Relative or absolute time display with automatic updates and locale-aware formatting.

Prior Art

Requirements

• MUST implement PFv6 visual designs
• MUST provide end-user feature parity with `@patternfly/react-core` Timestamp
• MAY adjust element API to leverage web platform strengths
• SHOULD maintain CSS custom property theming compatibility
• SHOULD expose useful CSS shadow parts

Element-specific considerations

• React `date` prop (Date object or parseable string) - map to `date` attribute (ISO 8601 string); parse internally
• React `dateFormat`: `full`, `long`, `medium`, `short` - uses `Intl.DateTimeFormat`
• React `timeFormat`: `full`, `long`, `medium`, `short`, or omit for date-only
• React `displaySuffix` - appended text (e.g. "UTC"); check if still in v6
• React `locale` - passed to `Intl.DateTimeFormat`; default to `navigator.language`
• React `tooltip` prop - shows full date/time in a tooltip; integrates with ``
• Renders `` for semantic HTML; `datetime` = ISO 8601

Checklist

Rename

• Delete `elements/pf-v5-timestamp/`
• Update `elements/package.json` exports
• Update `eslint.config.js` ignore globs if applicable
• Update docs `_snippets/` and `framework-integration/` references

Implementation

• API per `.claude/ADVICE.md`
• CSS uses v6 tokens, logical properties, nesting
• `@summary` and JSDoc on element class

Demos

• Demos match patternfly.org naming/structure
• CSS custom properties match computed styles from patternfly.org (Chrome MCP)
• Visual parity verified via Chrome MCP

Tests

• Public API covered (attributes, properties, events, slots)
• `a11ySnapshot` assertions

Reviews

• `/review-api` passes
• `/review-demos` passes
• `/review-a11y` passes
• `eslint` and `stylelint` pass

Ship

• Add changeset
• PR targets `staging/pfv6` (NOT `main`)