Track A.1: repoint microReticulum submodule at attermann upstream 0.3.0

Was: torlando-tech/microReticulum @ feat/t-deck @ ca355e5 (a torlando
fork with unrelated git history per pyxis_microReticulum_alignment_analysis).

Now: attermann/microReticulum @ tag 0.3.0 @ f8d91d1 (canonical upstream).

This commit is configuration-only — just the submodule pointer + URL.
Pyxis will not build yet because vanilla upstream doesn't ship the
fork's added subtrees (src/LXMF, src/BLE, src/Hardware/TDeck, src/UI,
src/Instrumentation, PSRAMAllocator/BytesPool/ObjectPool/FileStream/
FileSystem, Cryptography/{BZ2,Ratchet}, Utilities/Print,
SegmentAccumulator). Subsequent commits in this branch vendor those
into pyxis itself or carve them out into standalone libraries per
the alignment plan.

.gitmodules

@@ -1,4 +1,6 @@
 [submodule "deps/microReticulum"]
 	path = deps/microReticulum
-	url = https://github.com/torlando-tech/microReticulum.git
-	branch = feat/t-deck
+	url = https://github.com/attermann/microReticulum.git
+	# Pinned at the 0.3.0 release tag so the build is reproducible. Bump
+	# the pin deliberately when we want a newer microReticulum (and re-run
+	# the conformance suite to catch any drift).