Part of #2134 — Phase 3.

Spec: .local/specs/022-config-simplification/spec.md § Phase 3

Goal

Replace 6 parallel provider construction paths in bootstrap/provider.rs with a single function.

Current State

bootstrap/provider.rs contains:

• named_claude() — reads [llm.cloud] + secrets
• pcfg_claude() — reads OrchestratorProviderConfig + fallback to [llm.cloud]
• build_sub_provider("claude") — same with different entry point
• summary_claude() — reads model_spec string + fallback to [llm.cloud]
• Equivalent 4-way duplication for OpenAI, Gemini, Ollama

Tasks

• Implement build_provider_from_entry(&ProviderEntry, &Config) -> Result<AnyProvider>
• Rewrite create_provider() to dispatch on RoutingStrategy instead of ProviderKind
• Remove all named_*, pcfg_*, build_sub_provider, summary_* functions
• Update zeph-core/src/config.rs re-exports accordingly

Acceptance

• create_provider() uses only build_provider_from_entry()
• LLM serialization gate: live session test with orchestrator config before merge
• All 6397 tests green