feat(prompts): versioned prompt registry, v1 seed, pinning + stamping

Pipeline v2 Phase 1, commit 2/4. Prompt_Registry (read) +
Prompt_Registry_Writer (immutable create/activate/seed) over the new
prompts table; canonical v1 bodies extracted verbatim into
Prompt_Defaults(+Editorial) — single source for BOTH the seed migration
(Migrate_Prompt_Seed_V0180, flag-gated, self-healing) and the in-code
fallback, so a missing table renders byte-identical prompts and never
fatals. Call sites swapped: Content_Prompts, Analysis_Prompts,
Chief_Editor, LLM_Research_Provider. Includes the image-composer seam
keys image.rewriter_system + image.style_template (composer PR consumes,
must not add its own prompt storage).

Pinning: Cost_Tracker::set_run_id() registers the process run context,
ensures the runs ledger row, and pins active versions once per run;
log_api_call/log_image_generation stamp prompt_version (run pins) +
agent_role (stage map) on every generation_log row. Single-pass keeps
stage 'draft' and stamps content.single_pass explicitly.

Under-300 refactors: Content_Generator's four duplicated span/log blocks
consolidated into execute_stage() (301 -> 224 lines, behavior
identical); get_avg_tokens_for_stages body moved to Cost_Reporter with a
delegating wrapper kept for API compatibility.

Tests: byte-identical fallback renders (single_pass/outline/polish/
editor.system), token filling, key coverage incl. stage-map integrity.

Agent-Session: pipeline-v2-phase1-engineer-20260612

ARCHITECTURE.md

@@ -127,6 +127,7 @@ prautoblogger/
 ├── includes/
 │   ├── class-prautoblogger.php        # Main orchestrator — registers all hooks, delegates execution
 │   ├── class-pipeline-schema-installer.php # v0.18.0 substrate tables (prompts, run_sources, run_decisions, runs, run_stages)
+│   ├── class-migrate-prompt-seed-v0180.php # One-shot v0.18.0 prompt-registry seed migration
 │   ├── class-executor.php             # Cron handlers, generation AJAX (start + status), model registry
 │   ├── class-ajax-handlers.php        # Non-generation AJAX: images, models, test connections
 │   ├── class-generation-lock.php      # DB-level atomic mutex for single-writer generation
@@ -173,6 +174,12 @@ prautoblogger/
 │   │   ├── class-image-media-sideloader.php # Imports images into WordPress media library
 │   │   ├── class-cost-tracker.php     # Logs all API costs, enforces budget limits
 │   │   ├── class-stage-display-map.php # Stage vocabulary: labels + default roles + prompt keys (old + new + image stages)
+│   │   ├── class-prompt-registry.php  # Versioned prompt registry, read side (render, pins, self-healing fallback)
+│   │   ├── class-prompt-registry-writer.php # Registry write side (create version, activate, seed) — versions immutable
+│   │   ├── class-prompt-defaults.php  # Canonical v1 bodies: content.* + analysis.* (seed + fallback single source)
+│   │   ├── class-prompt-defaults-editorial.php # Canonical v1 bodies: editor.* / research.system / image.* (composer seam)
+│   │   ├── class-run-context.php      # Per-process active run id (set by Cost_Tracker::set_run_id)
+│   │   ├── class-run-state.php        # runs-table ledger + lifecycle row (ceiling/reserved/settled, pins, status)
 │   │   ├── class-logger.php           # Structured logging singleton (error/warning/info/debug)
 │   │   ├── class-article-worker.php   # Single-article generation (content + edit + publish)
 │   │   ├── class-pipeline-runner.php  # Orchestrates pipeline; chains per-article cron jobs