fix(vscode,intellij): handle missing status and fix StringIndexOutOfBoundsException in completion renderer

[octo-patch]

Summary

This PR fixes two bugs in the client extensions:

1. VSCode: Constant spinner when no completion model is running (fixes #4418)

Problem: When the Tabby server is connected but no completion model is configured, the status bar shows a persistent spinning animation. This happens because StatusBarItem.ts does not handle the codeCompletionNotAvailable status emitted by tabby-agent, so the icon stays as the loading spinner from the previous Starting state.

Solution: Add a codeCompletionNotAvailable case to the switch statement in StatusBarItem.ts that displays the warning icon with the appropriate tooltip — consistent with other warning states like rateLimitExceeded.

2. IntelliJ: StringIndexOutOfBoundsException in InlineCompletionRenderer (fixes #4404)

Problem: InlineCompletionRenderer.kt throws java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0 at line 95 (currentLineSuffix[0]) when suffixReplaceLength == 1 but currentLineSuffix is empty. This can happen when the completion item's replaceRange.end extends past the end of the actual document line (e.g., cursor at end of line or document state mismatch).

Solution: Guard the suffixReplaceLength == 1 branch with currentLineSuffix.isNotEmpty(). When the suffix is empty, the code falls through to the existing else block which handles the case gracefully without accessing out-of-bounds indices.

Test plan

• VSCode: Connect to a Tabby server with no completion model configured; verify the status bar shows a warning icon (⚠) instead of a spinning spinner
• IntelliJ: Verify no StringIndexOutOfBoundsException when inline completion is triggered at the end of a line

[ronda-labs]

Both bugs are the kind of defensive coding gap that's hard to write tests for upfront — a constant spinner when no completion model is configured is a bad first-run experience, and a StringIndexOutOfBoundsException in the renderer would make the IDE plugin look broken. The null check on status and the bounds guard on the completion text look correct. Does the VSCode fix also address the spinner state when the model endpoint changes at runtime, not just on initial connect?

[octo-patch]

Yes — StatusBarItem.update() is wired to this.client.status.on("didChange", () => this.update()) (StatusBarItem.ts:33), so whenever tabby-agent emits a status change at runtime (including when the model endpoint changes and codeCompletionNotAvailable is re-emitted), the new case fires and the icon transitions to the warning state. It's not gated on initial connect.