Provider-agnostic LLM registry, config check, migration runbook

[llm] assigns the bulk and editor roles by name over a [providers.*]
registry (kind = openai | anthropic, per-provider model, effort, daily
ceiling and price table); DeepseekBackend becomes OpenAiCompatibleBackend
(reasoning_effort passthrough), AnthropicBackend builds from the same
ProviderConfig, meters and provider_costs are keyed by provider name.
Gemini 3.8 Flash is declared via Google's OpenAI-compatible endpoint so
switching the editor is one line (or DAILY_EPUB_LLM__EDITOR=gemini for an
A/B dry run). Stale [deepseek]/[anthropic] tables, the top-level
max_daily_usd and the old key env vars fail loudly.

daily-epub config check validates and prints the resolved roles, models,
key presence and paths without opening the database.

docs/runbooks/curation-v2-migration.md walks the server upgrade from v1.

Registry implemented by a Claude agent from an orchestrator brief;
verified fmt/clippy(-W dead_code)/test green.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A1rCLQeKBgnBo3oTgHuTMe

src/curate/profile/mod.rs

@@ -624,7 +624,7 @@ mod tests {
         use std::sync::Arc;
 
         use super::super::llm::{MockBackend, UsageMeter};
-        use crate::config::DeepseekConfig;
+        use crate::config::ProviderConfig;
         use crate::types::{RatingEvent, TokenUsage};
 
         let dir = tempfile::tempdir().unwrap();
@@ -667,7 +667,7 @@ mod tests {
         let llm = LlmClient::with_backend(
             "deepseek-v4-flash",
             initial.text,
-            UsageMeter::new(&DeepseekConfig::default(), 2.0),
+            UsageMeter::for_provider(&ProviderConfig::deepseek()),
             backend.clone(),
         );
         let rebuilt = rebuild(&db, &llm, &opml, &profile_path, 60).await.unwrap();