chore(v0.8.1): version bump + CHANGELOG + ARCHITECTURE.md for reaper

Bump plugin header and PRAUTOBLOGGER_VERSION 0.8.0 → 0.8.1. Patch
bump — the reaper is internal infrastructure; no user-visible UX
change.

CHANGELOG:
- Fixed: orphan `llm_research` rows now reaped daily.
- Added: WP-CLI `wp prautoblogger reap-research`; `_prautoblogger_run_id`
  post_meta is now written by Publisher on every post.

ARCHITECTURE.md:
- Decision #13 (Run-ID based log linking) cross-refs the new post_meta.
- New Decision #19 documents the reaper's scan/amortize/delete policy,
  the 1-hour grace window, the 7-day stale cutoff, and the one-shot
  activator back-populate migration.

DB schema unchanged — no PRAUTOBLOGGER_DB_VERSION bump.

Final commit of the v0.8.1 bundle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,27 @@ All notable changes to PRAutoBlogger will be documented in this file.
 Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project uses [Semantic Versioning](https://semver.org/).
 
+## [0.8.1] — 2026-04-21
+
+### Fixed
+
+- **Orphaned LLM research costs now reaped daily.** When a pipeline died
+  between post creation and the final cost-amortization step (e.g.
+  execution-time kill on shared hosting), the `llm_research` row stayed
+  unlinked and the affected articles' cost popovers understated true spend.
+  A new daily cron (`prautoblogger_reap_orphan_research_rows`, 03:15
+  server time) retroactively amortizes orphan rows against posts from
+  the same run. Includes a one-time activator migration to back-populate
+  `_prautoblogger_run_id` post_meta for existing posts.
+
+### Added
+
+- New WP-CLI command `wp prautoblogger reap-research` for manual reaping
+  and ops debugging.
+- `Publisher::build_meta()` now writes `_prautoblogger_run_id` on every
+  generated post, so the reaper has a direct meta path from run_id to
+  sibling posts without walking `wp_prautoblogger_generation_log`.
+
 ## [0.8.0] — 2026-04-21
 
 ### Changed