chore: post-0.1.2 follow-up — codex P3 fix + README

[enriquephl]

Context

PR #20 (OpenRouter audit passthrough) shipped to the v0.1.2 prerelease without a codex-cli code review. This follow-up captures the codex review pass plus a README gap that landed alongside #20.

Both this follow-up and the upcoming model_config.toml fallback-array support will fold into the v0.1.3 cut. v0.1.2 stays as the audit-feature prerelease; v0.1.3 will be where the audit code matures (codex review applied + fallback array).

Codex review of 2b20dfa

`codex review --commit 2b20dfa` reported one P3:

The openrouter: call completed log only runs for chat requests that pass through pipeline::run. dreaming::classify_session and post_process::{extract_facts, extract_structured_insights} call openrouter.execute directly and only read resp.reply — their usage / generation_id / model fields are discarded. `docs/llm-audit.md` claims those background paths are covered by tracing; they weren't.

Fix:

• Extracted log_openrouter_usage(task, session_id, &resp) as pub(super) fn in pipeline/mod.rs.
• Called it from all 4 OpenRouter call sites with the appropriate task label (chat_companion, memory_extraction, or insight_extraction).
• Threaded session_id: Uuid through extract_insights → extract_facts / extract_structured_insights so insight extraction logs carry session correlation.

`docs/llm-audit.md`'s claim is now honest. No tracing payload format change for the foreground chat path; just the helper extraction.

README

README.md and README.zh.md:

• The /message[_async] bullet now lists both prompt_traits and audit with a link to docs/llm-audit.md / .zh.md.
• Configuration table gains rows for OPENROUTER_APP_REFERER and OPENROUTER_APP_TITLE.

Out of scope

• crates.io publish — still on 0.1.1 across the registry; no republish this cycle.
• New tag — none; HEAD stays as 0.1.2 with this commit on top.
• GHCR rebuild — skipped; deploy is straight from local source to fly.

Test plan

• cargo build --workspace clean
• cargo fmt --all -- --check clean
• cargo clippy --workspace --all-targets -- -D warnings clean
• cargo test -p eros-engine-core -p eros-engine-llm --lib — 51/51 green
• Post-merge: flyctl deploy --remote-only -a eros-engine from local source
• Manual smoke: trigger a dreaming or insight-extraction event on staging; confirm a new openrouter: call completed log line appears with task = "memory_extraction" or task = "insight_extraction" (previously only task = "chat_companion" appeared)

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