docs: update CHANGELOG + PROJECT.md for pSEO Engine

Records all Phase 1 deliverables: content gaps, data freshness,
health checks, generation job monitoring, 45 tests, bug fixes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,16 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 ## [Unreleased]
 
 ### Added
+- **pSEO Engine admin tab** (`/admin/pseo`) — operational visibility for the programmatic SEO system:
+  - **Content gap detection** — queries DuckDB serving tables vs SQLite articles to find rows with no matching article per language; per-template HTMX-loaded gap list
+  - **Data freshness signals** — compares `_serving_meta.json` export timestamp vs `MAX(updated_at)` in articles; per-template status: 🟢 Fresh / 🟡 Stale / 🟣 No articles / ⚫ No data
+  - **Article health checks** (HTMX partial) — hreflang orphans (EN exists, DE missing), missing HTML build files, broken `[scenario:slug]` references in article markdown
+  - **Generation job monitoring** — live progress bars polling every 2s while jobs run; stops polling on completion; error drilldown via `<details>`; dedicated `/admin/pseo/jobs` list page
+  - **`_serving_meta.json`** — written by `export_serving.py` after atomic rename; records `exported_at_utc` and per-table row counts; drives freshness signals in pSEO Engine dashboard
+  - **Progress tracking columns** on `tasks` table (migration 0021): `progress_current`, `progress_total`, `error_log`; `generate_articles()` writes progress every 50 articles and on completion
+  - 45 new tests covering all health functions + pSEO routes (access control, rendering, gap detection, generate-gaps POST, job status HTMX polling)
+
+
 - **Dual market score system** — split the single market score into two branded scores:
   - **padelnomics Marktreife-Score™** (market maturity): existing score, refined — only for cities
     with ≥1 padel venue. Adds ×0.85 saturation discount when `venues_per_100k > 8`.