[codex] add ChatGPT project sources support

[vgorlovi]

Summary

Add first-class ChatGPT Project Sources management in browser mode for both the CLI and MCP.

Closes #131.

What changed

• add --project-sources add|delete|replace|sync to the CLI
• add --source for delete/replace target names
• add shared browser automation for ChatGPT Project Sources operations
• add MCP project_sources with the same add/delete/replace/sync operations
• update browser/MCP/README docs for persistent Sources management
• add targeted tests for promptless project-sources runs and helper behavior

Why

Uploading files into a chat is not the same as managing a ChatGPT project's persistent Sources tab. This change adds a first-class path for project-source management instead of relying on chat attachments.

Implementation notes

• targets the ChatGPT project Sources surface directly in browser mode
• batches uploads in groups of 10 files to match the current ChatGPT Sources UI limit
• prefers the Sources panel's own hidden file input so uploads can bypass the OS file picker and work in terminal/headless flows
• falls back to dialog-scoped sources upload behavior when needed
• verifies add/delete outcomes against the Sources list itself

Validation

• pnpm vitest run tests/browser/projectSources.test.ts tests/cli/promptRequirement.test.ts
• pnpm vitest run tests/mcp.schema.test.ts tests/mcp/consult.test.ts
• pnpm typecheck
• pnpm build