Show a recorded demo and a diagram of how it works

[rustfuture]

• A short recording below the status note: the documented example-agent-runtime-gate maps four task results to Accept / Retry / Escalate (offline, mock evidence; same output as the README sample). Generated from docs/demo/runtime-gate.tape with VHS: vhs docs/demo/runtime-gate.tape.
• A Mermaid flowchart in "How it works": evidence → GuardedHybridComposer → safety veto / retry recovery / retry budget / quality index → Accept, Retry, Escalate. Each box names a real item: DeterministicEvidence, SemanticEvidence, EvidenceVector (crates/reflex-core/src/evidence.rs), GuardedHybridComposer, compute_clean_quality_index and the veto / retry branches (crates/reflex-policy/src/composer.rs), the three actions (crates/reflex-core/src/action.rs).
• No other text changed (checked line by line against main).