feat(contacts): refactor contacts

[ComputelessComputer]

Summary

Refactors the contacts system with a unified selection model and adds pin/ordering support for organizations.

Core changes:

• Replaced { selectedOrganization, selectedPerson } with a tagged union ContactsSelection ({ type: "person" | "organization", id })
• Added created_at, pinned, pin_order fields to organization schema (zod + tinybase)
• Added created_at to human schema
• New contacts-list.tsx component with combined pinned list (people + orgs), drag-to-reorder, and sort options
• Removed contacts permission check from calendar sidebar (no longer needed there)

Bug fixes (latest commit):

• Fixed invalid nested <button> elements in PersonItem and OrganizationItem components (both contacts-list.tsx and organizations.tsx) — outer buttons replaced with <div role="button">
• Added pin_order to organization and human frontmatter transforms (both toFrontmatter and fromFrontmatter directions) so pin order persists across sessions
• Fixed pin order calculation to use cross-table max (both humans + organizations) when pinning, so new pins always sort to the end of the combined list

Review & Testing Checklist for Human

• Tab state migration: The ContactsState shape changed from { selectedOrganization, selectedPerson } to { selected: ContactsSelection | null }. Verify that existing persisted tab states don't cause runtime errors on app load.
• Keyboard accessibility: The <button> → <div role="button"> change in three components should still support Enter/Space activation and tab focus. Manually test keyboard navigation through the contacts list.
• Pin order round-trip: pin_order defaults to 0 in organizationToFrontmatter / humanToFrontmatter for unpinned items. After a save+load cycle, unpinned items will have pin_order: 0 instead of undefined. Confirm this doesn't affect sort behavior (pinned items are filtered by pinned boolean, not pin_order).
• Drag reorder of mixed pinned contacts: Pin a mix of people and organizations, then drag to reorder. Verify order persists after navigating away and back.

Suggested test plan: Open the contacts tab, create a few people and organizations, pin some of each, reorder the pinned list via drag, close and reopen the app, and verify the order and selection state are preserved.

Notes

• The dprint fmt rustfmt errors are pre-existing (missing rustfmt component for the Rust toolchain) and unrelated to this PR.
• Transform tests were updated for created_at but don't explicitly assert pin_order round-trip — may want to add those.

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Link to Devin run: https://app.devin.ai/sessions/8172945c219e4a7689550c510b911cd7
Requested by: @ComputelessComputer

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 7 additional findings.

[ComputelessComputer]

@yujonglee made changes to contacts view that involves adding to tinybase.

[devin-ai-integration]

Devin Review found 3 new potential issues.

View 12 additional findings in Devin Review.

[devin-ai-integration]

Devin Review found 1 new potential issue.

View 13 additional findings in Devin Review.

[devin-ai-integration]

Devin Review found 4 new potential issues.

View 16 additional findings in Devin Review.