Update authentication docs

[JulienLavocat]

Description of Changes

• Add an "Authentication" section under "Core concepts"
• Add an introduction about how and explanations about common topics
• Move claims usage out of SpacetimeAuth docs
• Update SpacetimeAuth docs to the new version of the dashboard

API and ABI breaking changes

None.

Expected complexity level and risk

2

Testing

Tested locally using Docusaurus

[JulienLavocat]

/update-llm-benchmark

[clockwork-labs-bot]

LLM Benchmark Results (ci-quickfix)

Language	Mode	Category	Tests Passed	Pass %	Task Pass %
Rust	rustdoc_json	basics	19/27	70.4%	66.7%
Rust	rustdoc_json	schema	23/34	67.6%	60.0%
Rust	rustdoc_json	total	42/61	68.9%	63.6%
C#	docs	basics	27/27	100.0%	100.0%
C#	docs	schema	18/34	52.9%	60.0%
C#	docs	total	45/61	73.8%	81.8%

_{Generated at: 2026-01-14T10:50:55.061Z}

[JulienLavocat]

/update-llm-benchmark