Fix OpenCode pane scroll input and registry hydration

[danshapiro]

Summary

• add provider-declared terminal behavior metadata for renderer and scroll-input policy resolution
• translate OpenCode wheel and touch scrolling into cursor-key input when the pane is in alt-screen mouse-capture mode
• stabilize extension-registry hydration by deduping concurrent loads, scoping waits to providers that use extension metadata, and clearing stale metadata when the server instance changes
• add unit, integration, and e2e regression coverage for the new behavior and hydration paths

Testing

• npm run check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Load extension registry before resolving non-OpenCode behavior

useEnsureExtensionsRegistry is now gated by providerUsesExtensionTerminalBehavior, which only returns true for opencode. For any other CLI extension that sets cli.terminalBehavior (the new manifest field added in this commit), a terminal-only startup path never triggers /api/extensions, so providerBehavior stays at defaults and the declared renderer/scroll policy is ignored. This means restored or directly-opened third-party extension terminals can silently run with the wrong behavior until the user manually opens another view that happens to load the registry.

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