chore(docs): regenerate llms-full.txt

[rickcrawford]

Summary

• `release-checks.yml`'s "llms-full.txt is current" gate failed on the v1.10.0 tag: the auto-regen-on-push workflow was removed in Fix the failing llms-full refresh, restore the README badges, and attribute what ships in the binary #925, so the corpus needs a manual regen before each tag now, and PRs Verify that a doc's shown output still matches what the code produces #927/Take the planning tree out of docs/, and stop leaking tracker ids #928 landed docs changes since the last regen.
• Regenerated `docs/llms-full.txt` via `scripts/regen-llms-full.sh`.
• Folded in docs: restructure features hub, link all examples, and extract dedicated pages for advanced features #931 (features-hub restructure), which landed on main after this branch was cut, and regenerated the corpus a second time to cover it.
• Renamed `docs/mcp-archestra-guardrails.md` -> `docs/mcp-gateway-guardrails.md` and tightened its intro. Updated all in-repo references (`docs/README.md`, `docs/features.md`, `docs/mcp.md`, `docs/use-case-mcp-federation.md`) and the `include_str!` path in `crates/sbproxy-core` plus a doc comment in `crates/sbproxy-extension` that pointed at the old name.

Test plan

• `bash scripts/regen-llms-full.sh --check` passes
• `bash scripts/check-doc-drift.sh` passes
• `cargo check -p sbproxy-core -p sbproxy-extension`
• `cargo fmt --all -- --check`
• CI green