Curation v2 step 6: Behind the paper, stats, run report block, lock

Behind-the-paper chapter (behind.xhtml, both editions) built from the run's
StageCounts and candidate_runs near misses; daily-epub stats [--days N];
StageCounts gains knn/feed gates and verdicts_in_prompt, timings split
into summaries + brief, the four-line §15.4 info block logged once per
run and printed by print_report; src/lock.rs flock guard on
<database_path>.lock for generate, profile rebuild, features backfill and
backfill-social; README updated for the new CLI, env vars and costs.

Implemented by a Claude agent from docs/plans/curation-v2-briefs/step6.md;
reviewed against plan §5, §15.

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

src/epub/templates/README.md

@@ -8,12 +8,13 @@ the crate root points askama here (`dirs = ["src/epub/templates"]`).
 |---|---|---|
 | `base.xhtml` | — | Shared XHTML skeleton (`{% block body_class %}`, `{% block content %}`) |
 | `cover_page.xhtml` | `CoverPage` | Page that displays the rasterized cover image |
-| `front_page.xhtml` | `FrontPage` | "From the Editor" + issue stats line |
+| `front_page.xhtml` | `FrontPage` | "The Brief" + issue stats line |
 | `in_this_issue.xhtml` | `InThisIssue` | Introduction chapter: per-section linked index |
-| `section.xhtml` | `SectionPage` | Section title page + LLM intro |
+| `section.xhtml` | `SectionPage` | Section title page (name only) |
 | `chapter.xhtml` | `ArticleChapter` | Article: header, body, rating/read-online footer |
 | `discussion.xhtml` | `DiscussionChapter` | Comment chapter (§3.7); body from `comments::render_xhtml` |
 | `world_briefing.xhtml` | `WorldBriefingChapter` | Wikipedia Current Events (§3.8), body from `world::render_xhtml` |
+| `behind.xhtml` | `BehindChapter` | "Behind the paper": run counts, admission mix, near misses, models (§15.1) |
 | `colophon.xhtml` | `ColophonChapter` | Back matter: models, cost, counts |
 | `cover.svg` | `CoverSvg` | Typographic cover, rasterized with resvg + tiny-skia |
 | `style.css` | — | Standard-edition stylesheet, embedded as `stylesheet.css` |

src/epub/templates/behind.xhtml

@@ -0,0 +1,20 @@
+{% extends "base.xhtml" %}
+{% block body_class %}behind{% endblock %}
+{% block content %}
+      <h1>Behind the paper</h1>
+      <p class="fact-line">{{ summary_line }}</p>
+      <p class="fact-line">{{ admitted_line }}</p>
+      <p class="fact-line">{{ learned_line }}</p>
+      <h2>Near misses</h2>
+      <p class="fact-line"><em>Highest utility not selected.</em></p>
+{% if near_misses.is_empty() %}
+      <p class="fact-line">None recorded for this run.</p>
+{% else %}
+      <ul class="near-misses">
+{% for line in near_misses %}
+        <li>{{ line }}</li>
+{% endfor %}
+      </ul>
+{% endif %}
+      <p class="fact-line">{{ models_line }}</p>
+{% endblock %}