feat(page): add page archive command

[0xble]

Summary

• add page archive using the official API fallback path
• accept page URLs and page IDs for archive targets
• fail fast with the existing setup guidance when no official API token is configured
• document the new command and auth requirement in the README and bundled skill
• add focused tests for archive success, URL/ID input handling, invalid target input, and missing token behavior

Usage examples

notion-cli page archive https://www.notion.so/workspace/My-Page-12345678abcdef1234567890abcdef12  # archive by URL
notion-cli page archive 12345678-abcd-ef12-3456-7890abcdef12                                      # archive by page ID

$ notion-cli page archive https://www.notion.so/workspace/My-Page-12345678abcdef1234567890abcdef12  # no API key configured
✗ create official API client: official API token is required (run 'notion-cli auth api setup' or set NOTION_API_TOKEN)

Partial follow-up for #17.

Validation

• go build ./...
• go test ./...
• golangci-lint run
• local CLI QA against a mock official API:
  • archive by URL returns ✓ Page archived
  • archive by ID returns ✓ Page archived
  • requests hit PATCH /v1/pages/<id> with {"in_trash":true}

[0xble]

Maybe worth adding unarchive / restore as follow-up, but I scoped this one to archive only