Add configurable provider instances

[batkiz]

Summary

This PR introduces configurable provider instances, allowing the same coding-agent provider to be added multiple times with different launch configurations.

Each instance has:

• a stable identity
• a custom display name
• an enabled state
• an optional binary override
• per-instance environment variables

For example, multiple Codex instances can use different CODEX_HOME values, allowing separate accounts and configurations to coexist without changing Waku's process-wide environment.

Motivation

Some coding agents use environment variables to select their configuration or account. Codex, for example, resolves configuration, authentication, sessions, and skills through CODEX_HOME.

Previously, Waku modeled each coding agent as a single global provider. Supporting multiple configurations would therefore require switching the environment outside Waku or duplicating provider-specific logic.

Provider instances keep the existing ProviderKind responsible for driver behavior and capabilities, while making launch configuration instance-specific. This also makes the feature usable by providers other than Codex.

Changes

• Add a persisted ProviderInstance configuration with a stable ID, custom name, provider kind, enabled state, binary override, and environment.
• Preserve the existing built-in providers and legacy settings format.
• Add native and web settings UI for creating, naming, configuring, enabling, disabling, and removing custom instances.
• Carry the provider instance identity through sessions, model selection, favorites, persistence, probes, catalogs, usage data, and provider process pools.
• Apply the selected instance environment to provider discovery and launch paths.
• Isolate provider-sensitive caches and long-running processes by instance.
• Resolve Codex-specific paths such as sessions, authentication, skills, and usage from the selected instance environment.
• Update protocol bindings and translations.

Backward compatibility

Existing settings and sessions continue to use the built-in provider instance whose ID matches the provider ID.

The existing disabled_providers and provider_binary_overrides settings remain supported, so no configuration migration is required.

Custom instances cannot shadow built-in IDs, and legacy sessions without an explicit provider instance ID fall back to their original provider.

Testing

• cargo test --lib
  • 342 application tests passed
  • 59 protocol tests passed
  • 24 environment-dependent tests ignored
• cargo check --bin waku
• bun test apps/web/src
  • 130 tests passed
• bun run --cwd apps/web typecheck
• cargo run -p waku-protocol --bin export_types -- --check