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

includes/class-migrate-prompt-seed-v0180.php

@@ -0,0 +1,59 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * phpcs:ignore WordPress.Files.FileName.InvalidClassFileName -- class naming convention differs from WordPress standard
+ *
+ * One-shot v0.18.0 migration — seed the versioned prompt registry.
+ *
+ * What: Writes the canonical hardcoded prompt texts (content, analysis,
+ *       editor, research, illustration rewriter, image Style Template)
+ *       into `wp_prautoblogger_prompts` as immutable version 1 and
+ *       activates them. Idempotent twice over: gated by the
+ *       `prautoblogger_migrated_prompt_seed_v0180` flag AND seed_v1()
+ *       itself skips any key that already has rows. The flag is only set
+ *       when the table was actually reachable, so a failed seed
+ *       self-heals on the next activation / version-mismatch pass.
+ *       Standalone class per the Migrate_Remove_Cloudflare_V0100
+ *       precedent (keeps Activator under the 300-line cap).
+ * Who triggers it: PRAutoBlogger_Activator::activate() — on activation and
+ *       on every db-version mismatch.
+ * Dependencies: PRAutoBlogger_Prompt_Registry(_Writer), get_option.
+ *
+ * @see class-activator.php                       — Sole caller.
+ * @see core/class-prompt-registry-writer.php     — seed_v1() implementation.
+ * @see includes/class-migrate-remove-cloudflare-v0100.php — Pattern precedent.
+ */
+class PRAutoBlogger_Migrate_Prompt_Seed_V0180 {
+
+	/** Option flag marking the seed as complete. */
+	private const FLAG = 'prautoblogger_migrated_prompt_seed_v0180';
+
+	/**
+	 * Run the seed once.
+	 *
+	 * Side effects: up to 12 INSERTs into the prompts table, one INFO log
+	 * line, one option write.
+	 *
+	 * @return void
+	 */
+	public static function run(): void {
+		if ( get_option( self::FLAG ) ) {
+			return;
+		}
+		if ( ! PRAutoBlogger_Prompt_Registry::is_available() ) {
+			return; // Table missing — retry on the next migration pass.
+		}
+
+		$seeded = PRAutoBlogger_Prompt_Registry_Writer::seed_v1( 'seed:v0.18.0' );
+
+		if ( class_exists( 'PRAutoBlogger_Logger', false ) ) {
+			PRAutoBlogger_Logger::instance()->info(
+				sprintf( 'Prompt registry seeded: %d key(s) written as v1.', $seeded ),
+				'activator'
+			);
+		}
+
+		update_option( self::FLAG, '1' );
+	}
+}