[codex] Add V8 code browser build

[cla7aye15I4nd]

What changed

• add a dedicated V8 project definition using the canonical V8 checkout and depot_tools
• build the release v8_monolith target with ICU and external startup data disabled
• generate a source-only compilation database for SCIP indexing
• allow per-project timeout, build parallelism, and ccache size while retaining safe defaults for existing projects

Why

V8 is a high-value untrusted JavaScript and WebAssembly parser/runtime used by Chromium. It is intentionally handled as a large-project exception and will only be merged if the real CI build, SCIP index, compressed pack, and browser smoke test stay within the repository's resource limits.

Local validation

• parsed the project YAML
• syntax-checked its embedded build block
• Actionlint
• frontend JavaScript syntax check

The draft PR is the real resource and compatibility test.