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

tools/config-lint/Cargo.toml

@@ -2,7 +2,7 @@
 name = "warden-config-lint"
 version = "0.1.0"
 edition = "2021"
-description = "Static target-config checks for WardenOS: catch memory-map faults (the 0x40000 MCU-load brick class) and other flash-time config mistakes before a flash, not on the bench."
+description = "Static target-config checks for the Luckfox Pico 86 Panel: catch memory-map faults (the 0x40000 MCU-load brick class) and other flash-time config mistakes before a flash, not on the bench."
 license = "GPL-2.0-only"
 
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