fix: update skills for core/ removal, new subsystems, and provider routers

[slin1237]

Problem

The smg-dev-guide skills had drifted from the smg codebase. A full audit (all skill files vs. smg@a18d64f5) found:

• model_gateway/src/core/ was removed upstream, leaving dead paths (core/routing/, core/steps/worker/local/) in the map, contribute, review-pr, and three recipes.
• Subsystems built since the guide was written had zero coverage: priority scheduler, multi-tenancy, rate limiting, memory, and the Anthropic/Gemini provider routers.
• New components missing from the map: crates skills and blob_storage, the tui dashboard, clients/{python,java,openapi-gen} + the make generate-clients pipeline.
• Wrong counts/types: reasoning "10+ families" (actually 8), grpc_client/data_connector key types.

Solution

Systemic fixes to the always-loaded skills (map, implement, contribute, review-pr, anti-patterns) plus the dead-path renames in affected recipes. The 10 recipes that need full body rewrites are deferred but now tracked — with the key correction for each — in a new Recipe Freshness table in implement/SKILL.md.

Changes

• skills/map/SKILL.md: add crates skills + blob_storage, tui, clients/{python,java,openapi-gen}; new "Subsystems Inside model_gateway" section (scheduler, multi-tenancy, rate limiting, memory, provider routers, worker lifecycle); Anthropic/Gemini in request flow; fix key types + counts; add make generate-clients
• skills/implement/SKILL.md: "Subsystems without a dedicated recipe yet" + "Recipe Freshness" tables
• skills/contribute/SKILL.md, skills/review-pr/SKILL.md, skills/review-pr/anti-patterns.md: core/ path renames, new subsystem rows, circuit_breaker_can_execute()
• skills/implement/{routing-policy,grpc-backend,discovery-feature}.md: dead core/ path fixes
• README.md: recipe counts aligned with the map

Affected Skills

• smg:map
• smg:contribute
• smg:review-pr
• smg:implement
• Recipe files (routing-policy, grpc-backend, discovery-feature)
• Command router (smg.md)
• Plugin config (plugin.json)

Checklist

• Follows conventional commit title format
• Commit(s) are signed off (git commit -s)
• Tested with claude plugins add . locally
• Skill triggers correctly on intended prompts
• No broken @file.md references in skills

Note: this is a content refresh verified by auditing every path/type/count against the smg source tree (not runtime-tested), so the "tested locally / skill triggers" boxes are left unchecked. The 10 major recipe bodies (flagged in the new Recipe Freshness table) still need full rewrites in a follow-up.