Add project get and update commands

[jacobwgillespie]

Summary

• add depot projects get with text and JSON output
• add partial depot projects update support for names, regions, and cache storage policies
• preserve cache retention when changing a project's cache storage limit
• resolve projects from arguments, flags, environment variables, or depot.json
• document the new commands and cover their API requests with tests

Testing

• go test -race ./pkg/cmd/projects
• go test ./...
• go vet ./...
• go build ./cmd/depot
• go mod tidy (no diff)

Linear Issue: DEP-5490

  

[linear-code]

DEP-5490

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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[cursor]

Approved. Cursor Bugbot and Cursor Security Agent both completed successfully with no unresolved findings needing human review; chatgpt-codex-connector also finished. No reviewer assignment tool was available, so no reviewers were assigned.

  

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