feat(network-proxy): add MITM support and gate limited-mode CONNECT (#9859)

## Description
- Adds MITM support (CA load/issue, TLS termination, optional body
inspection).
- Adds `codex-network-proxy init` to create
`CODEX_HOME/network_proxy/mitm`.
- Enforces limited-mode HTTPS correctly: `CONNECT` requires MITM,
otherwise blocked with `mitm_required`.
- Keeps `origin/main` layering/reload semantics (managed layers included
in reload checks).
- Centralizes block reasons (`REASON_MITM_REQUIRED`) and removes
`println!`.
- Scope is MITM-only (no SOCKS changes).

gated by `mitm=false` (default)

codex-rs/network-proxy/Cargo.toml

@@ -16,6 +16,7 @@ anyhow = { workspace = true }
 async-trait = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
 codex-utils-absolute-path = { workspace = true }
+codex-utils-home-dir = { workspace = true }
 codex-utils-rustls-provider = { workspace = true }
 globset = { workspace = true }
 serde = { workspace = true, features = ["derive"] }