cli: rename profile v2 flag to --profile (#23883)

## Why

Profile v2 is taking over the user-facing profile selection path, so the
CLI no longer needs to expose the transitional `--profile-v2` spelling.
This switches the public args surface to `--profile` before the
remaining legacy profile plumbing is removed separately.

## What

- Rebind `--profile` and `-p` to the v2 profile name argument that
selects `$CODEX_HOME/<name>.config.toml`.
- Stop parsing the legacy shared CLI profile argument while keeping its
implementation path in place for follow-up cleanup.
- Update CLI validation, profile-name parse errors, and the
legacy-profile collision message/tests to refer to `--profile`.

## Testing

- `cargo test -p codex-cli -p codex-config -p codex-protocol -p
codex-utils-cli`

codex-rs/utils/cli/src/shared_options.rs

@@ -31,11 +31,11 @@ pub struct SharedCliOptions {
     pub oss_provider: Option<String>,
 
     /// Configuration profile from config.toml to specify default options.
-    #[arg(long = "profile", short = 'p')]
+    #[arg(skip)]
     pub config_profile: Option<String>,
 
     /// Layer $CODEX_HOME/<name>.config.toml on top of the base user config.
-    #[arg(long = "profile-v2")]
+    #[arg(long = "profile", short = 'p')]
     pub config_profile_v2: Option<ProfileV2Name>,
 
     /// Select the sandbox policy to use when executing model-generated shell