docs: improve documentation quality

[cmilesio]

What

• Clarify the App model, ownership, command surfaces, request validation, and runtime operations across the documentation.
• Synchronize library projections and their generator language, add content-audit coverage, and compact Makefile help output.
• Add Lighthouse product presentation and safety-focused performance benchmark guidance.

Why

The site should present one consistent App workflow, keep generated projections aligned with their sources, and make benchmark rollout risks explicit.

[cmilesio]

Superseded by independent PRs based directly on main:

• chore: standardize the docs Makefile workflow #15 Makefile workflow
• test: strengthen the documentation content audit #16 content audit
• docs: align documentation navigation labels #17 navigation labels
• docs: strengthen application guidance #18 application guidance
• docs: strengthen App composition guidance #19 App composition guidance
• docs: clarify data and persistence workflows #20 data and persistence
• docs: strengthen developer tool guidance #21 developer tools
• docs: refine frontend starter kit guidance #22 frontend starter kits
• docs: strengthen operations guidance #23 operations
• docs: clarify framework reference surfaces #24 reference
• docs: refresh library guidance #25 libraries
• docs: strengthen testing guidance #26 testing
• docs: refine async and runnable scenario guidance #27 async and runnable scenarios

Together these reconstruct this PR's content changes, with refreshed source-backed proof statistics.