KiBot's -s/--skip-pre SKIPS the named preflight, so `erc: kibot ... -s erc`
skipped ERC and ran DRC, and `drc: ... -s drc` did the reverse. Both checks
still ran, but every violation was reported under the wrong job name -- which
is exactly what made a broken DRC look like a passing one.

KiCad's stock default severity for footprint_symbol_mismatch is `warning`
(board_design_settings.cpp:189), and KiBot's DRC preflight only fails on
errors. So `schematic_parity: true` ran the check and could never fail it --
a mismatch was reported on every CI run for months, buried in ~100 warnings,
and every run went green.

Raising it to `error` makes the parity gate real.

KiCad 10 added a Local History feature. On first save it creates
<project>/.history and calls git_repository_init() on it, so the directory is
a nested git repository. KiCad writes a .gitignore inside it, but that governs
KiCad's own history repo -- this repo still sees an embedded repository and
reports it untracked. Committing it would add a broken gitlink.

These parts exist in KiCad-Master-Lib; the boards referenced libraries that no
longer exist (kml-custom, KML-Custom, and SparkFun libraries that never
contained the part) or names the library has since changed.

KiCad embeds footprint geometry in the .kicad_pcb, so the boards rendered and
fabricated correctly and the rot stayed invisible -- it only surfaces on
update-from-library, or when a generator tries to resolve a nickname.

Nickname/name only. No geometry is changed:

  SparkFun-LED:WS2812-5050-4PIN -> KMLib_IC_SMD:WS2812-5050-4PIN
  kml-custom:AP63205WU-7 -> KMLib_IC_Power:AP63205WU-7_Buck_Regulator
  kml-custom:CUI_SJ-3524-SMT -> KMLib_Connectors:CUI_SJ-3524-SMT
  kml-custom:SOIC_05WU-7_DIO -> KMLib_IC_SMD:SOIC_05WU-7_DIO
  kml-custom:Thermal Pad -> KMLib_Mounting:Thermal_Pad

Only references that failed to resolve were touched. Generic parts (<=4 pins)
and KiCad *-rescue libraries are deliberately excluded: fingerprint matching
cannot distinguish a 2-pin resistor from a 2-pin capacitor, so those are being
done by hand.

- add the validate-board job: KiCad 10 format, a real (error-severity) DRC
  parity gate, every library reference resolving, un-swapped Makefile targets,
  and .history/.kicad_prl gitignored. Green means the board is done.
- run on pull_request, not just push to main. Hardware checks previously ran
  only AFTER a change had merged: they could report that main was broken, but
  never stop it from breaking. A gate that only fires post-merge is a
  notification, not a gate.
- pin bread-infra to v1.0.0 rather than @main, so a bread-infra commit cannot
  silently change what this PR is gated on.

KiCad 10 adds design-block libraries and generates a design-block-lib-table
alongside fp-lib-table and sym-lib-table. Like those, it holds absolute paths,
so it is machine-local and generated -- never committed.

Also ignores KiCad's project lock file (~<project>.kicad_pro.lck), written
whenever a project is open.

The existing .gitignore predates KiCad 10 and covered neither, so simply opening
a board left the working tree dirty.

The library re-point renamed symbols in lib_symbols from LIB:OLD to LIB:NEW,
but a symbol's sub-units carry the bare item name:

    (symbol "KMLib_IC_Power:AP63205WU-7_Buck_Regulator"
        (symbol "AP63205_0_1" ...)      <- still the old prefix

KiCad requires every sub-unit to be named "<parent item>_<unit>_<style>", so any
symbol whose ITEM name changed (not merely its library) failed to load:

    Invalid symbol unit name prefix AP63205_0_1

Rename each sub-unit to match its parent. Nickname-only re-points were never
affected -- their item name is unchanged.

Note kicad-cli reports "Failed to load schematic" and still EXITS 0, so this was
invisible to CI and to a scripted ERC sweep. Only the GUI surfaced it.

v1.1.0 adds the schematic-load check. kicad-cli prints 'Failed to load
schematic' and still exits 0, so an unloadable schematic scored as zero ERC
violations -- 34 boards were unopenable while every automated check said they
were fine. validate-board now runs in the KiCad container and actually loads
every sheet.

config.kibot.yaml had drifted into five variants across the fleet. Three differed
only in trailing comments; the two real variants are 2-layer and 4-layer.

Adopts bread-infra templates/config.kibot.2-layer.yaml, chosen from the board's
actual copper layer count (2).

Also pins bread-infra to v1.2.0, which adds a validate-board check that a board
must plot every copper layer it has.