docs: Document platform-scoped arch and libc overrides for TOML schemas

[SMK1085]

Documents the [platform.<os>.arch] and [platform.<os>.libc] schema settings added in moonrepo/plugins#151: a new "Platform overrides" section with the buf example (global remap + Linux identity override), resolution-order notes, the archs-restricts-vs-arch-renames distinction, and customization pointers on the {arch}/{libc} token list. No <VersionLabel> added since the feature isn't tied to a proto release yet — happy to add one at release time.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Documents new platform-scoped overrides for {arch} and {libc} token mappings in the non-wasm plugin configuration, clarifying precedence and adding an example.

Changes:

• Adds platform.<os>.arch and platform.<os>.libc settings to the platform settings list.
• Updates token docs to reference both global (install.*) and platform-scoped (platform.<os>.*) mappings.
• Adds a new “Platform overrides” section with precedence rules, example config, and clarification vs archs.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

#### 🎉 Hooray! `codspeed-rust` just leveled up to 5.0.1!

A heads-up, this is a breaking change and it might affect your current performance baseline a bit. But here's the exciting part - it's packed with new, cool features and promises improved result stability 🥳!
Curious about what's new? Visit our releases page to delve into all the awesome details about this new version.

⚡ 5 improved benchmarks
❌ 1 regressed benchmark
✅ 17 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	hash_files[1000]	10.5 ms	15.9 ms	-34.23%
⚡	WallTime	load_one	40.1 ms	27.8 ms	+44.11%
⚡	WallTime	load_many	58.1 ms	41.5 ms	+40.13%
⚡	WallTime	get_file_hashes[1000]	6.6 ms	4.7 ms	+39.36%
⚡	WallTime	get_file_hashes[100]	1.7 ms	1.2 ms	+36.7%
⚡	WallTime	load_all	134.5 ms	100.9 ms	+33.34%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing SMK1085:docs-schema-platform-arch-overrides (3898aee) with master (ab3dc07)}