feat: scaffold cc app entrypoint + manifest (refs #540)

[rwrife]

Summary

• add user/apps/cc/main.c scaffold with stable --help/--version behavior
• return deterministic non-zero diagnostic for compile attempts while TinyCC freestanding wiring is still pending
• add staged app manifest user/apps/cc/manifest.json (shape pinned to manifests/apps_dev_cc.json)
• add help cc resource entry (user/apps/os/help/resources/cc.txt) and list it in the help index

Why this slice

This is a starter slice for #540 that makes the cc app surface concrete and reviewable without claiming full compile/link execution yet.

Test Plan

• ./build/scripts/test.sh apps_dev_cc_manifest
• ./build/scripts/validate_manifests.sh user/apps/cc/manifest.json

Follow-ups

• wire cc into disk-image staging at /apps/dev/cc
• integrate/port manifest_resolution.c runtime path for freestanding app linking
• add host/qemu command-behavior tests for cc --help / cc --version and compile-path diagnostics

Refs #540