feat: issue create / refresh / dispatch commands and CLI entry point

[shouze]

Summary

Three subcommands (issue create, issue refresh, issue dispatch), the $EDITOR helper, output formatters, and the main CLI entry point.

Tasks

• src/output/format.ts — buildEpicBody, buildSubIssueBody, buildPlanTable, bodyLengthWarning, splitBodyAtLimit, printDispatchSummary
• src/tui/editor.ts — openEditor(content), resolveEditor() (respects $VISUAL → $EDITOR → vi)
• src/commands/create.ts — issue create action: stdin → EPIC issue + overflow comment
• src/commands/refresh.ts — issue refresh action: diff + update + metadata patch
• src/commands/dispatch.ts — issue dispatch action: plan table + per-repo sub-issues
• github-issue-ops.ts — Commander entry point, --non-interactive, --dry-run, upgrade command

Body overflow handling

When body > BODY_LIMIT (65 000 chars):

• issue create → hard error unless --non-interactive (truncates + posts overflow as comment)
• issue refresh → silently truncates + posts overflow as comment

Acceptance criteria

• bun run build succeeds
• ./dist/github-issue-ops --help shows all commands
• ./dist/github-issue-ops issue create --help lists all flags
• --dry-run prints body without calling GitHub API