feat(llq): add snip library for 5G xHaul Low-Latency QoS JVD

[KB-x]

What's New

Snip library for the Low-Latency Queueing (5G xHaul) validated design — 66 files covering the complete QoS + transport + service stack.

• 36 EVO snips (ACX7509/7100/7024, PTX10001) + 27 Junos snips (MX204/480/304)
• Headline: priority low-latency hardware scheduler (ACX-only) for sub-10µs eCPRI queuing
• 7 categories: CoS, firewall, transport, services, policy, interfaces, OAM
• Full cross-reference headers (Seen-on, Pair-with, Highlights)
• Topology registry + variables reference + README

Why

LLQ is the most complex CoS design in the JVD repo (8-class model, 5 distinct CoS binding patterns, MAC-based eCPRI MFC filters). Extracting it as a snip library makes the design reusable and auditable.

Details

• snips/evo/cos/: 17 files — FC, 4 classifiers, 4 rewrites, 3 scheduler variants, scheduler-map, 5 binding patterns
• snips/junos/cos/: 12 files — same minus ACX-only bindings (IRB, L2 fronthaul, static FC)
• snips/*/firewall/: MFC IPv4/IPv6 DSCP-to-FC filters + eCPRI MAC-based CCC filter
• snips/*/transport/: IS-IS (interface + global/SR), MPLS, BGP labeled-unicast, hash-key, load-balance
• snips/*/services/: EVPN-VPWS-MH, EVPN-ELAN, BGP-VPLS virtual-switch, L3VPN-IRB
• snips/*/policy/: PPLB, ALLOW_LOOPBACK, SR_NONZERO_LOOPBACKS, next-hop-self
• snips/evo/interfaces/: LAG + ESI for EVPN multi-homing
• snips/evo/oam/: CFM maintenance-domain (802.1ag continuity-check)
• _topology_registry.json: 12 devices mapped to 64 snips by role
• _variables.md: 40+ template variables documented with examples

Testing

• All 64 .conf snip bodies verified against source configs in conf/
• Scheduler split confirmed: ACX uses low-latency, PTX/MX use strict-high
• Device classification validated via stanza presence scanning