refactor(cli): extract parseFlags helper from 302-line main()

[la14-1]

Why: main() at 302 lines is the largest uncovered function; flag-parsing extraction reduces it by ~220 lines and isolates all argument handling.

Summary

• Extract parseFlags() async function that handles all global flag parsing and returns a typed ParsedFlags object
• Extract reusable helpers: extractBooleanFlag, extractEnvFlag, extractValueToEnv, extractValue, validateBetaFeatures
• main() reduced from 302 lines to 84 lines (72% reduction)
• Zero behavioral changes — all flag parsing, env var setting, config loading, and validation preserved exactly

Test plan

• bunx @biomejs/biome check src/ passes with zero errors
• bun test passes (2106/2108, 2 pre-existing flaky failures in digitalocean-token.test.ts unrelated to this change)
• Verified main() line count: 302 → 84

-- spawn-refactor/complexity-hunter

[la14-1]

Rebased onto main to resolve merge conflicts. Added --repo flag extraction (from #3360) to the parseFlags helper to keep it in sync with main.

-- refactor/pr-maintainer

[la14-1]

Rebased onto main to resolve merge conflicts. Integrated the initFeatureFlags() call and fast_provision experiment code (from #3366) into the parseFlags helper. Lint and tests pass (2 pre-existing failures, same as main).

-- refactor/pr-maintainer

[la14-1]

This PR has been open for 4+ days with all CI checks passing (ShellCheck, Biome Lint, Unit Tests, Mock Tests, macOS Compatibility — all SUCCESS). It is mergeable with no conflicts.

Requesting human review when convenient.

-- spawn-refactor/pr-maintainer

[la14-1]

Rebased onto main to resolve merge conflict from #3371 (narrowed fast_provision experiment to images-only). Updated the parseFlags helper to match: betaFeatures.push("images") instead of "tarball", "images". Lint passes, tests pass (2 pre-existing flaky failures, same as main).

-- refactor/pr-maintainer

[la14-1]

This PR is ready for review. All CI checks pass and there are no merge conflicts.

-- refactor/pr-maintainer

[la14-1]

Rebased onto main (was 4 commits behind). Clean rebase, no conflicts.

-- refactor/pr-maintainer

[la14-1]

Verified in worktree: tests pass (2236/2238, same 2 pre-existing failures as main), lint clean (biome 0 errors). PR is mergeable and ready for review.

-- refactor/pr-maintainer