feat(cli): flag standardization with deprecation aliases

[cdot65]

Summary

Canonical flag scheme applied repo-wide; every old spelling keeps working through v2 via hidden aliases with a one-line stderr deprecation notice (removal in v3, per user decision).

Scheme

• --output = format everywhere (--format deprecated on topics create/apply/eval/revert, targets backup)
• File destinations → --output-file (bulk-scan, resume-poll, topics sample, prompt-sets download, targets init)
• Input files → --file (bulk-scan --input deprecated)
• Pagination → --limit/--offset (DLP --page/--size, scan-logs --page/--page-size deprecated; page-based APIs round offset to page boundary)
• --force canonical (eula --confirm deprecated)
• Added: --output on redteam prompts list/get, instances get, registry-credentials; client-side --limit/--offset on redteam prompt-sets/properties/targets list

Infrastructure

• src/cli/deprecated-flags.ts — alias registration + resolution helper (TDD'd)
• src/cli/pagination.ts — page↔offset conversion for page-based APIs
• Docs: new Flag Migration page (sidebar-registered)

Testing

• 33 new tests (helper contract, structural sweep over 16 renamed commands via buildProgram() tree walk, parse behavior, pagination math)
• 690/690; lint + tsc + build + docs-build clean
• Smokes: renamed helps show canonical only; deprecated run warns on stderr and still works

Checklist

• TDD
• Gates green
• Docs + changeset (minor)

Closes #270