Feat: add upload model command

[Zatiji]

Adds tracel model upload <name> <directory>: walks a local directory, checksums each file, requests presigned multipart upload URLs from Tracel Console, and uploads all file parts to S3 in parallel with progress reporting. It's important to note that SymbolicPaths are silently ignored inside the directory we want to upload from.

• Creates the target model interactively if it doesn't already exist (with an optional description prompt).
• Streams SHA-256 checksums and part offsets locally, validating the backend's presigned-URL response (part sequence/gaps and total-size) before any upload starts.
• Uploads parts across a fixed worker pool with fail-fast cancellation on the first error.

Test plan

• Unit tests for file collection/checksumming, part-task building (including malformed responses), and multipart upload (success + failure paths)
• Manual end-to-end run against dev server: new model, existing model (new version), model-not-found cancel path

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.