ide: the attiny85 beside the atmega328p, one directory each

The presets cover both parts, so the solution should too. Studio carries
avrdevice as a project property, so a part is a project rather than a
configuration, and both build example/main.cpp to a .text byte-identical to
their CMake counterpart: 1242 B on the mega, 1212 B on the tiny, each with the
architecture its own object file says.

They need separate directories, not just separate names. Studio builds into
<project dir>/<Configuration> whatever OutputDirectory claims — setting it per
project creates the directory and then ignores it — so two projects in one
directory share example/main.o. Verified rather than assumed: with both in ide/,
the single shared object read avr:25 while the mega's ELF read avr:5, so a
build of one after the other without a rebuild links the wrong part's object.

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

.gitignore

@@ -2,8 +2,8 @@ build/
 .cache/
 
 # Atmel Studio: generated per machine, its build outputs, and per-user state
-ide/*.componentinfo.xml
-ide/Debug/
-ide/Release/
+ide/*/*.componentinfo.xml
+ide/*/Debug/
+ide/*/Release/
 ide/.vs/
 ide/*.log