feat(ai): consolidated OpenAI-family streaming and add OpenRouter API support

This change introduces a new `openrouter` API type and extensively refactors OpenAI-family streaming providers, centralizing shared logic and improving robustness.

Key changes include:
- **Unified OpenAI-family Logic:** Consolidated core utilities, compat resolution, request shaping, and stream processing into `openai-shared.ts`, reducing duplication across `openai-completions`, `openai-responses`, and `openai-codex-responses`.
- **OpenRouter API Type:** Introduced a dedicated `openrouter` API type with dual-surface compatibility, allowing it to dispatch requests as either OpenAI Chat Completions or Responses.
- **Enhanced Provider Integration:**
    - Improved Perplexity search to leverage shared OpenAI streaming transports, including API-key fallback to OpenRouter and support for Perplexity's Responses API.
    - Integrated xAI-specific logic directly into the shared `stream.ts` dispatch, removing the dedicated `xai-responses` provider.
    - Refined credential parsing for Google Gemini CLI and handling of Azure deployment names.
- **Robustness & Consistency:** Improved error handling for Codex, standardized output token parameter resolution, and ensured consistent application of reasoning suppression across all Chat Completions dialects.
- **New Documentation:** Added `provider-endpoint-constraints.md` to detail endpoint-specific behaviors and quirks for various providers.
- **Telemetry & Debugging:** Extended telemetry propagation to advisor calls and overflow compaction tasks. Improved debugging for Codex WebSocket failures and stream error messages.
- **Tooling & Security:** Updated browser stealth scripts to prevent detection and added a new `ts-no-inline-cast-access` TTSR rule.

docs/providers.md

@@ -4,7 +4,7 @@ Providers are the model backends `omp` can route requests to: Anthropic, OpenAI,
 
 A **provider** is the account or backend namespace, such as `anthropic`, `openai`, `google`, or `ollama`. A **model** is a concrete model under that provider, selected as `provider/model-id`, such as `anthropic/claude-opus-4-6`. Disabling a provider removes every model under it from selection; if you only want to narrow individual models, use model settings instead.
 
-This page covers how providers become available, how credentials are resolved, the provider/environment-variable map, local engines, disabling providers, and custom providers. For model selection and the full `models.yml` schema, see [Model and Provider Configuration](./models.md). For config-file locations and merge precedence, see [Settings](./settings.md). For credential storage and login flows in depth, see [Secrets and credentials](./secrets.md). For the complete environment-variable reference, see [Environment variables](./environment-variables.md). For local engine setup, see [Local models](./local-models.md). For context-file discovery providers, see [Context files](./context-files.md).
+This page covers how providers become available, how credentials are resolved, the provider/environment-variable map, local engines, disabling providers, and custom providers. For endpoint-specific request, reasoning, tool, stream, usage, and retry constraints, see [Provider endpoint constraints](./provider-endpoint-constraints.md). For model selection and the full `models.yml` schema, see [Model and Provider Configuration](./models.md). For config-file locations and merge precedence, see [Settings](./settings.md). For credential storage and login flows in depth, see [Secrets and credentials](./secrets.md). For the complete environment-variable reference, see [Environment variables](./environment-variables.md). For local engine setup, see [Local models](./local-models.md). For context-file discovery providers, see [Context files](./context-files.md).
 
 ## How `omp` decides a provider is available