docs: add platforms overview index and custom evergreen setup guide

[AIdrifter]

Add a single centralized overview index (site/docs/development/index.md) providing:

• A comparison matrix of supported platforms (Linux, Android TV, RDK, Docker tooling).
• A 3-stage recommended development workflow.
• Custom Evergreen path configurations and parameter mapping reference table for SoC partners.
• Step-by-step guide for SoC partners to build and compress custom debug Cobalt Core packages locally using host lz4_compress.

Bug: 537982944

[github-actions]

🤖 Gemini Suggested Commit Message

---

docs: Add development index and Evergreen guide

Add a centralized development overview index to improve the developer
onboarding experience. This includes a comparison matrix of supported
platforms, recommended workflows, and detailed configurations for
Evergreen path mapping. It specifically provides SoC partners with
instructions for building and compressing custom debug Cobalt Core
packages locally.

Bug: 537982944

---

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[gemini-code-assist]

Code Review

This pull request introduces a new development and build platforms overview document (cobalt/site/docs/development/index.md) for Cobalt, detailing supported platforms, recommended workflows, and custom Evergreen setup instructions. Feedback was provided to correct the GN build target from cobalt_loader to cobalt lz4_compress to properly compile the Cobalt Core shared library and ensure the availability of the compression tool.

[gemini-code-assist]

The target cobalt_loader is incorrect. In Cobalt's Evergreen architecture, the target to compile the Cobalt Core shared library (libcobalt.so) and its resources is cobalt (or cobalt_install), whereas loader_app is the target for the loader executable itself. Since this step is intended to generate libcobalt.so and the resource files, the target should be updated to cobalt. Additionally, explicitly building the host tool lz4_compress ensures it is available for the optional compression step below.

Suggested change

	autoninja -C out/<platform>_devel cobalt_loader
	autoninja -C out/<platform>_devel cobalt lz4_compress