Add dropweb Mihomo RU Cascade template (auto-failover)

[enkinvsh]

What

New MIHOMO subscription template by-dropweb/subscription-templates/mihomo-ru-cascade.yaml + registry entry in subscription-templates-list.json.

Why another RU template

Unlike the existing select-based templates, routing here is fully automatic — users never pick a server manually:

• ▶️ YouTube / 💬 Discord → fallback [🌀 Cascade → ⚡ Fastest]: cascade nodes (RU-entry → EU-exit) preferred; automatic failover to the fastest direct node when the cascade dies; automatic return when it recovers
• 🌍 VPN → fallback [⚡ Fastest → 📶 First Available] — emergency net when the whole main pool is down
• REJECT sentinel keeps an empty Cascade group honestly DEAD (no live COMPATIBLE stub), so the template degrades gracefully on panels without cascade nodes — YouTube/Discord simply ride ⚡ Fastest

Health-check parameters verified against mihomo core sources

Documented in the template header:

• uniform expected-status: 204 across all groups sharing one health-check url — per-url alive state is stored keyed by url (adapter.go), mixed criteria cause alive flapping between groups
• parent group url must match child group url, otherwise the child gets falsely marked dead for the parent
• large intervals (60-120s) + lazy: true are safe because failover is event-driven (groupbase.go onDialFailed: real-traffic failures trigger an immediate health check) — battery-friendly on mobile without losing switching speed
• timeout: 8000 on the cascade path — a 2-hop probe under load doesn't fit the default 5s, causing false DEAD → flapping

RU specifics

• fake-ip + respect-rules DNS, DoT direct resolvers, bootstrap DNS with fallbacks resilient to DoH blocking
• QUIC UDP/443 reject with a Discord-voice exception (no-resolve logic rule, voice on UDP/443 keeps working)
• legiz ru-bundle / re:filter rule-sets, Android exclude-package list, rules ordered so RU domains match without forced DNS resolution

Cascade node-name filters are clearly marked for operators to adjust (>>> ПОМЕНЯЙТЕ ПОД СЕБЯ <<<); comments are in Russian, consistent with the other RU templates.

Running in production on our fleet (dropweb.org).