Add invocation flag to disable the auto-updater per-run

[WiggidyW]

Today the only way to disable the auto-updater for a single binary invocation is to set the OBJECTIVEAI_SKIP_UPDATE env var. Add a native CLI flag so it's discoverable via --help and doesn't require shell-env wrapping.

Scope

All four binaries that link the shared updater carry the updater feature:

• objectiveai-cli (objectiveai-cli/src/main.rs)
• objectiveai-api (objectiveai-api/src/main.rs)
• objectiveai-mcp (objectiveai-mcp-cli/src/main.rs)
• objectiveai-viewer (objectiveai-viewer/src-tauri/src/main.rs)

Each calls objectiveai_sdk::updater::maybe_auto_update(...) from within a #[cfg(feature = "updater")] block. The check that gates execution today lives in objectiveai-sdk-rs/src/updater.rs::imp::run:

if std::env::var_os(SKIP_ENV_VAR).is_some() {
    emit_notification(
        config.handle.as_ref(),
        Updater::Skipped { reason: SkipReason::OptedOut },
    ).await;
    return Ok(());
}

Suggested approach

1. Add a flag — --no-update (or --skip-update) — at the binary level. Recognized BEFORE the binary's own argument parsing (or as a global pre-parse step) so the updater check sees it before any per-binary handling kicks in.
2. When set, short-circuit the call to maybe_auto_update entirely (skip the function call rather than going through the env-var check). Emits the same Skipped { reason: OptedOut } notification so consumers see consistent JSONL.
3. Keep the env var as the secondary path; the flag is for discoverability + scripting ergonomics. (Same precedence rule as the parallel issue Promote all env vars to clap arguments across cli / api / mcp / viewer #181: CLI > env.)
4. Pre-parse implementation: scan args for the flag before passing it through to clap. Strip it from argv so downstream parsers don't see it.

Why

• --help discoverability — currently the only way to learn about the opt-out is by reading source.
• Test ergonomics — every integration test wanting a stable update behavior currently sets OBJECTIVEAI_SKIP_UPDATE=1 in the environment.
• Symmetric with the existing OBJECTIVEAI_SKIP_UPDATE env var which is set by the re-exec'd child to break update loops.

Cross-binary interaction

The CLI's update-check fires self-update for the CLI; api/mcp/viewer have their own. A --no-update flag passed to the CLI does not affect api/mcp/viewer if launched separately. Each binary owns its own flag. No cross-binary fan-out.

Out of scope

• Removing the env var (stays as the secondary source).
• Changing the updater's behavior in any other way.
• Modifying the per-binary marker file scheme.

Related

• Promote all env vars to clap arguments across cli / api / mcp / viewer #181 — env-vars → clap migration (this flag is one specific instance of that broader refactor; tracked separately because it's the most user-visible knob and may want to ship first as a smaller change).