Add distro/ubuntuCore for UC26 snap and image builds.

Centralize salmanoff snapcraft, dangerous-model image scripts, and QEMU
workflow so UC26 can be reproduced from the SMO repo without ubuntu-core-practice.

Co-authored-by: Cursor <cursoragent@cursor.com>

distro/ubuntuCore/config/dev-image.env.example

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+# Copy to config/dev-image.env and adjust after setup-dev-signing.sh.
+#
+# ACCOUNT_ID comes from: snapcraft whoami  (or snap whoami when logged in)
+# SIGN_KEY_NAME comes from: snap keys  (after snapcraft create-key + register-key)
+
+ACCOUNT_ID=
+SIGN_KEY_NAME=salmanoff-dev
+
+# System user created on first boot (no Ubuntu One / console-conf SSO).
+SYSTEM_USER_NAME=smo
+SYSTEM_USER_EMAIL=smo-dev@salmanoff
+# Public key used in the system-user assertion (private key stays local).
+SSH_PUBKEY_FILE=config/ssh/smo-dev.pub
+
+# Dangerous-grade dev model (UC26 amd64). salmanoff is optional until --snap is passed.
+MODEL_NAME=salmanoff-dev-amd64

distro/ubuntuCore/config/qemu-stock.env

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+# Defaults for scripts/run-qemu.sh (source manually if you want overrides)
+RAM_MB=2048
+SMP=2
+SSH_PORT=8022
+OVMF_CODE=/usr/share/OVMF/OVMF_CODE_4M.secboot.fd
+OVMF_VARS_TEMPLATE=/usr/share/OVMF/OVMF_VARS_4M.ms.fd

distro/ubuntuCore/config/snap-source.env.example

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+# Optional: remote git source if snapcraft.yaml is switched from local tree to git.
+SMO_GIT_URL=git@zbz-gitea-as-hayodea:hayodea/salmanoff.git
+SMO_GIT_BRANCH=clast