docs: reposition as the 86 Panel development environment

The repo's documentation framed it as a support repo for one product
(WardenOS). Since going public the real audience is anyone with a Luckfox
Pico 86 Panel: a maintained 6.18 kernel, an off-device development loop,
and a device simulator that exist nowhere else for this board. Reframe the
README and top-level docs board-first, with WardenOS documented as the
downstream consumer it is (ADR-0008).

Also an editorial pass over the whole doc set:
- every H1/H2 is now a short title, not a sentence (ADRs, qemu/, patches/,
  drivers/, architecture, NPU feasibility, config-lint, payload); workflow
  flowchart titles fixed at the source in tools/flowgen.py and regenerated
  with fresh bench numbers
- README Quick Start commands verified against the scripts; requirements
  corrected (curl, bare python, gcc >= 14) and the MC/DC gate added as a
  step (run green locally on gcc 14.2)
- dropped the 'needs python (not python3)' vendor dig: build-kernel.sh
  inherited the same requirement (filed #10 to remove it)
- glossed MC/DC and HPMCU on first use; marked the tests/uboot-ab
  reference as flare-edge; deduplicated the three-simulator list into the
  root README table

sim/bench.json

@@ -0,0 +1,7 @@
+    Finished `bench` profile [optimized] target(s) in 0.08s
+     Running benches/sim_bench.rs (target/release/deps/sim_bench-57835de7b7b68615)
+{"bench":"hpmcu_tick","ns_per_op":1.8,"iters":1000000}
+{"bench":"cru_poll","ns_per_op":21.4,"iters":1000000}
+{"bench":"modbus_read_holding","ns_per_op":73.7,"iters":1000000}
+{"bench":"rga_improcess","ns_per_op":6.7,"iters":1000000}
+{"bench":"membus_poke_peek","ns_per_op":27.0,"iters":1000000}