issue create should show the sequential issue number in output #8

Context#

When using the CLI to create an issue, the success output currently shows the AT Protocol TID (record key) as the issue identifier:

✓ Issue created: #3mejsg3jglw2m
  Title: PR Phase 1: ...
  URI: at://did:plc:.../sh.tangled.repo.issue/3mejsg3jglw2m

The #3mejsg3jglw2m is an opaque AT Protocol TID, not the human-readable sequential issue number (#4). To view or reference the issue afterwards, you need tangled issue view 4, but nothing in the creation output tells you what that number is. This forces an extra tangled issue list call just to find the assigned number.

This is especially disruptive in agent/LLM workflows where the result of one command is used as input to the next (e.g. "create an issue, then immediately view it to confirm").

Tasks#

• After creating an issue, compute the sequential issue number and include it in the success output.
• Output format should clearly show both the sequential number and the URI, e.g.:

  ✓ Issue created
    Number: #4
    Title: PR Phase 1: ...
    URI: at://did:plc:.../sh.tangled.repo.issue/3mejsg3jglw2m
  

• Ensure --json output also includes the sequential number field (e.g. "number": 4).
• Add or update tests to verify the number appears in both human and JSON output.

Notes#

The sequential number is 1-based and determined by the issue's position when listed. The tangled issue list command already resolves this ordering — the same logic should be reusable here.