feat(cli): support ALIEN_PROJECT env var for --project

[ab-alien-dev]

Summary

• Adds env = "ALIEN_PROJECT" to the CLI's global --project flag, matching the existing ALIEN_API_KEY/ALIEN_WORKSPACE pattern.
• Lets callers that prefer environment variables (e.g. the ai-agent sandbox, which already resolves and passes --project explicitly per invocation) set the project once via env instead of a flag on every call.

Test plan

• Additive change to an existing Option<String> field's input sources — no behavior change when the env var is unset.
• cargo build -p alien-cli / relevant CLI tests pass in CI.

[greptile-apps]

Greptile Summary

The PR adds ALIEN_PROJECT as an environment-backed source for the global project option and normalizes blank or whitespace-only values before platform project resolution.

• Preserves linked-project and interactive fallback when ALIEN_PROJECT is blank.
• Trims surrounding whitespace from nonblank global project values.
• Adds focused unit coverage for both normalization cases.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
crates/alien-cli/src/lib.rs	Adds the environment-backed global project input and applies blank-value normalization at its sole execution-context consumption point.

_{Reviews (2): Last reviewed commit: "Fix greptile" | Re-trigger Greptile}