dev: add DEV_UNLIMITED mock worker and UI toggle for local dev proxy

[SaintD1smas]

Adds DEV_UNLIMITED mock SSE in worker, dev_server.js, and UI toggle in CompanionPanelView and CompanionManager to allow local testing against a dev proxy (no real API calls). Intended for local development only.

[Qodo-Free-For-OSS]

Hi, The dev worker base URL is accepted from a free-form text field and stored without validation, but both ClaudeAPI and ElevenLabsTTSClient force-unwrap URL(string:), so malformed input can crash the app when clients are recreated.

Severity: action required | Category: reliability

How to fix: Validate URL before saving

Agent prompt to fix - you can give this to your LLM of choice:

Issue description

Dev proxy URL is user-entered and stored without validation, but downstream clients force-unwrap URL initialization, which can crash the app.

Issue Context

User input flows: CompanionPanelView TextField → CompanionManager.setDevWorkerBaseURL → workerBaseURL → ClaudeAPI(proxyURL: ...) / ElevenLabsTTSClient(proxyURL: ...) → URL(string:)!.

Fix Focus Areas

• leanring-buddy/CompanionManager.swift[140-154]
  • Validate trimmed with URLComponents/URL (require http/https scheme, host present) before persisting.
  • If invalid, do not update UserDefaults and expose an error state to the UI.
• leanring-buddy/ClaudeAPI.swift[17-20]
  • Replace force-unwrap with throwing init or graceful error.
• leanring-buddy/ElevenLabsTTSClient.swift[23-25]
  • Replace force-unwrap with throwing init or graceful error.
• leanring-buddy/CompanionPanelView.swift[651-697]
  • Display validation error and disable Save when invalid.

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