docs+tools: workflow flowchart harness (P4) + drivers Tier-1/Tier-2 split

- tools/flowgen.py: generates docs/workflows/<name>.md — one outcome-first mermaid
  flowchart per workflow the SDK tests (hpmcu watchdog, modbus read, cru ladder,
  rga offload, relay drive, freshness contract), each stamped with its benchmark
  ns/op or 100% MC/DC result. Deterministic; reads the cargo-bench trend json.
- drivers/README.md: honest Tier-1 (relays + freshness, 100% MC/DC here now) vs
  Tier-2 (modbus/rga — serious testing + fault-injection + benchmarks via sim
  models; driver sources migrate in with the flare-edge unification) per ADR-0002/0005.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017wB8KB3MMQztRDXCMCkPrf

docs/workflows/rga-offload.md

@@ -0,0 +1,15 @@
+# RGA 2D offload dispatch
+
+> **Outcome tested:** Blits go to the RGA when it succeeds, and fall back to the CPU when it doesn't.
+
+**Benchmark** (`rga_improcess`): 7.2 ns/op
+
+```mermaid
+flowchart TD
+  A[draw request] --> B{RGA compiled in\n(#if WARDEN_USE_RGA)?}
+  B -- no --> C[LVGL software draw]
+  B -- yes --> D[improcess src,dst,rects IM_SYNC]
+  D --> E{IM_STATUS == SUCCESS?}
+  E -- yes --> F[done on RGA]
+  E -- no --> C
+```