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

CHANGELOG.md

@@ -27,6 +27,28 @@ behavior change** to the Economy (single-pass) and multi-step publish paths.
   per-stage default agent role and primary prompt-registry key.
 - Uninstall now drops the five substrate tables and clears every plugin cron hook
   (previously only two of eight were cleared).
+- **Versioned prompt registry** (`PRAutoBlogger_Prompt_Registry` + `_Writer`): all pipeline
+  prompt copy — content system/single-pass/outline/draft/polish, analysis system/user,
+  editor system/review, research system, plus the **illustration rewriter prompt and the
+  image Style Template** (the image-composer PR seam) — is seeded as immutable version 1
+  from the v0.16.0 hardcoded texts (`prautoblogger_migrated_prompt_seed_v0180`). One active
+  version per key; changes create new versions, never mutate. Call sites render through the
+  registry with a **byte-identical in-code fallback** when the table is missing/empty
+  (self-healing, no fatals on half-migrated state). No admin UI in Phase 1.
+- **Prompt-version pinning**: `Cost_Tracker::set_run_id()` pins the active version of every
+  key on the run's row; every generation_log row (text and image stages) is stamped with the
+  pinned `prompt_version` plus a stage-derived `agent_role`. Single-pass rows keep stage
+  `draft` and stamp `content.single_pass` explicitly.
+- `PRAutoBlogger_Run_State` (runs-table ledger row: ceiling/reserved/settled/overage, pins,
+  sticky lifecycle states) and `PRAutoBlogger_Run_Context` (per-process run id, mirrors the
+  Opik trace-context pattern).
+
+### Changed
+- `Content_Generator`'s four stage methods now share one `execute_stage()` helper (the Opik
+  span + dispatch + cost-log boilerplate was identical); file drops from 301 to ~220 lines.
+  No behavior change: same prompts, models, params, span names, stage values.
+- `Cost_Tracker::get_avg_tokens_for_stages()` body moved to `Cost_Reporter` (read-only
+  reporting query); the Cost_Tracker method remains as a delegating wrapper.
 
 ### Fixed
 - ARCHITECTURE.md documented the multi-step edit stage as `edit`; the code has always