feat: support stack names in bulk commands

[omattsson]

Summary

• Replace parseBulkIDs (integer-only) with resolveBulkIDs that runs each element through resolveStackID, accepting stack names, UUIDs, and numeric IDs
• All four bulk commands (deploy, stop, clean, delete) now accept names just like single-stack commands
• Deduplication operates on resolved IDs, so my-stack and 42 deduplicate if the name resolves to 42
• Early bounds check prevents unnecessary API calls when >50 inputs are provided

Behavioral notes

• bulkClean and bulkDelete now create the client and resolve names before the confirmation prompt (fail-fast on auth/resolution errors rather than prompting first)

Test plan

• All existing bulk command tests pass (table/JSON/YAML/quiet output, positional args, mixed args, API errors)
• New unit tests for: stack names, UUIDs, mixed names+IDs, name dedup, unknown name error
• Edge cases: empty input, commas-only, whitespace, >50 items
• Full test suite green (go test ./...)

Closes #41

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