docs: refresh project context

[twilightsaurus]

Summary

Refreshes current project documentation after the audit-remediation closure and milestone-tag backfill.

• updates AGENTS.md from the old TinyFugue/VPS-only description to the current client-neutral local/remote node architecture
• updates the documented npm run check coverage to include shared-adapter and Mudlet validation
• removes stale hard-coded v0.2.1 "latest release" wording from the top-level and VPS installation guides
• records the newly backfilled Slice 17–23 milestone tags in the roadmap

Historical audit and remediation-closure records remain unchanged.

Validation

• Prettier: passed
• git diff --check: passed
• docs references: 399 references across 47 Markdown files
• version validation: 0.2.8 across 23 locations
• protocol: 64 passed
• desktop: 152 passed
• relay: 226 passed
• shared adapter: 31 passed
• Mudlet: 32 passed
• TinyFugue: 101 passed
• cross-component relay E2E: passed
• frontend production build: passed
• full npm run check: passed