build: the libavr pin advances past phase 6, at byte parity everywhere

The pin crosses libavr's phase 6 - the renamed system surface, the named
serial configs, the receiver-tolerance table, the paged SPM receipts -
and every loader image comes out size-identical: the full matrix on six
representative chips (the exhaustive cross product on three of them),
the stock and autobaud columns untouched, the four tsb tiers back on
their recorded floors at 510/526/638/836.

Byte parity was not free, and the two libavr defects it surfaced were
fixed there rather than absorbed here. The EEPROM write procedure's
step 2 - the SPMEN spin - had landed unconditionally and cost every
build six bytes for a wait a polled loader can never take; it is scoped
now, and the loaders state the datasheet's own omission clause
(spm_interlock::omitted, DS40002061B 8.6.3). The blocking page
erase/write grew an internal wait the tiers' settle() already provides,
so the tiers issue the command form and pureboot keeps its host-driven
sp_spm path.

What the port states rather than inherits: the stock 115200 at 16 MHz
sits +2.1 % past the receiver-tolerance table libavr now holds rates
to, so the hardware links say .allow_baud_error = true - the same
2.5 % envelope pureboot_baud_feasible() has always enforced, proven on
silicon across the fleet. rx_ready() reads readable() now.

Alongside the pin: rule 33's ASCII sweep over every source (docs keep
their typography), rule 34's InsertBraces in .clang-format with the
tree reformatted, std::array over the simavr runners' raw buffers, and
the stale Studio size in ide/README.md replaced by the claim its
check-flags gate actually holds.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tools/check.sh

@@ -1,9 +1,9 @@
 #!/bin/bash
-# The port's gate: every chip's generated workflow — build, size matrix, and
+# The port's gate: every chip's generated workflow - build, size matrix, and
 # the simulator-driven protocol suites. --full adds the reflect-spot builds
 # (libavr's rule: reflect compiles are bounded to its spot set, never the
 # full matrix) and swaps the compact size matrix for the exhaustive
-# clock × baud × backend cross product. libavr resolves from the `libavr/`
+# clock x baud x backend cross product. libavr resolves from the `libavr/`
 # submodule; LIBAVR_ROOT overrides it for a working tree.
 set -e
 cd "$(dirname "$0")/.."
@@ -36,7 +36,7 @@ if ((full)); then
 	done
 fi
 
-# Every tree is freshly built now — the one moment the README's size table
+# Every tree is freshly built now - the one moment the README's size table
 # can be held to what the images measure (a per-preset ctest sees only its
 # own chip; the table needs all of them, and ungated it drifts: a
 # common-code shave moves every row at once with nothing over budget).