feat(runs): state machine, idempotent resume, reaper extension, retention

Pipeline v2 Phase 1, commit 4/4. Run_Stage_State persists per-run
per-stage state keyed run_id + stage + agent_role + item_key (item_key
scopes articles because one run_id spans a whole batch; agent_role is
the Phase-2 quorum dimension, schema-only). Done stages snapshot output
and are reused on re-entry — writer stages via
Content_Generator::set_run_item, the review via its stored verdict, a
published item skipped outright — never re-run, never re-charged. Post
creation is keyed by _prautoblogger_run_id + new _prautoblogger_idea_hash
(check-before-insert in Publisher) so retries cannot duplicate posts.
Run-level research/analysis checkpoints + done/failed lifecycle marks
ride Pipeline_Runner/Executor (incl. orphan-abort + budget-abort paths).

Run_Reaper rides the EXISTING #19 daily cron: stages stuck running >2x
expected stage wall-clock and runs silent >2x expected run wall-clock ->
failed (filterable), open stages reaped, queryable as 'incomplete'.
Retention: request_json + stage output payloads NULLed after R days, R
from the new Audit Payload Retention setting (default constant 14,
0 = keep forever, no literal at point of use). Audit_Writer records
editorial verdicts (run_decisions) and per-article kept sources
(run_sources) for new runs.

Under-300: status-transient/summary helpers extracted verbatim to
Pipeline_Status (Pipeline_Runner 271; removed the worker's duplicate).

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

includes/admin/class-settings-fields-extended.php

@@ -113,6 +113,16 @@ class PRAutoBlogger_Settings_Fields_Extended {
 				'step'        => '0.01',
 				'description' => __( 'Hard stop when reached. 0 = unlimited.', 'prautoblogger' ),
 			),
+			array(
+				'id'          => 'prautoblogger_request_json_retention_days',
+				'label'       => __( 'Audit Payload Retention (days)', 'prautoblogger' ),
+				'type'        => 'number',
+				'section'     => 'prautoblogger_schedule',
+				'default'     => PRAUTOBLOGGER_DEFAULT_REQUEST_JSON_RETENTION_DAYS,
+				'min'         => 0,
+				'step'        => '1',
+				'description' => __( 'Heavy audit payloads (request_json on the generation log, stage output snapshots) are emptied after this many days by the daily cleanup cron. Cost/token rows are kept forever. 0 = keep payloads forever.', 'prautoblogger' ),
+			),
 			array(
 				'id'          => 'prautoblogger_per_run_cost_ceiling_usd',
 				'label'       => __( 'Per-Run Cost Ceiling (USD)', 'prautoblogger' ),