fix(vscode): default Agent Manager terminals to the side panel

[marius-kilocode]

What Problem This Solves

Agent Manager opens terminals in VS Code by default even when no destination has been configured. Users must select the Agent Manager panel before they can keep terminal work beside their sessions.

Why This Change Was Made

Use the embedded side panel as the default in the extension setting, host resolver, and webview startup state. Keep the existing preference precedence: a saved panel choice wins over the application setting, and explicit settings win over the default. Do not migrate or rewrite preferences just because a terminal is opened.

User Impact

• Users with no configured destination get the Agent Manager panel from the terminal button and Focus Terminal shortcut. Run and worktree Setup scripts also follow this destination.
• Existing VS Code terminal and Agent Manager choices remain unchanged, including after reload. Invalid settings retain the VS Code fallback.
• This changes the default only, not PTY platform support or transport behavior. Existing musl Linux, native Windows ARM64, and remote WebSocket limitations are unchanged. There is still no automatic fallback after embedded terminal startup or connection failure; affected users must select VS Code terminal manually.

Evidence

• Extension unit suite: 4,510 passed, 1 skipped, 0 failed. The broader terminal subset has 108 passing tests.
• Extension build, typecheck, lint, Knip, Kilo ownership guard, and patch whitespace checks passed.
• Isolated macOS VS Code: confirmed the preference was absent, checked the default menu selection, opened a working embedded shell, selected VS Code terminal and opened it, then reloaded and confirmed that selection persisted.
• Windows, Linux, and remote hosts were not manually verified in this change.

Unconfigured default:

Explicit VS Code choice after reload:

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (7 files)

• .changeset/agent-manager-terminal-default.md
• packages/kilo-vscode/package.json
• packages/kilo-vscode/src/agent-manager/terminal-destination.ts
• packages/kilo-vscode/tests/unit/agent-manager-terminal-destination.test.ts
• packages/kilo-vscode/tests/unit/agent-manager-terminal-side.test.ts
• packages/kilo-vscode/tests/unit/extension-arch.test.ts
• packages/kilo-vscode/webview-ui/agent-manager/terminal/side.ts

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_{Reviewed by grok-4.6 · Input: 63.9K · Output: 10.1K · Cached: 363.9K}

_{Review guidance: REVIEW.md from base branch main}