[codex] Centralize CLI argument parsing

[rushillshah]

Scope

• move duplicated CLI option parsing into lib/args.js
• use the shared parser in the main CLI, terminal UI, and graph review entrypoints
• preserve repeated options consistently and add focused parser coverage

Partially addresses #11.

Validation

• npm run check
• node --test tests/args.test.mjs (2 passed)
• graph-ai estimate smoke against examples/sample-vault
• noninteractive UI smoke
• npm pack --dry-run includes lib/args.js
• npm test: focused changes pass; full suite retains the known date-window baseline failures tracked by Tests use stale dated fixtures and fail as time advances #23 / green draft PR [codex] Stabilize rolling-window test fixtures #25. A later rerun also hit a missing linked dependency in this isolated worktree, so CI is the authoritative full-suite result.

Risk

Low. The shared parser preserves the main CLI behavior and makes repeated options consistent in the UI and graph review entrypoints.

[rushillshah]

Maintenance blocker (2026-07-19): focused parser tests, npm run check, CLI smokes, and npm pack --dry-run pass. Both CI jobs fail only on the same four date-sensitive baseline tests tracked by #23 and fixed in green draft PR #25 (67 passed / 4 failed here). Next action: review and merge #25, then rerun this PR CI; keep #28 draft until checks pass and review is complete.