Initial import of Shirobana bot backend

Include utility modules, shared channels, prompts, read-only skills, wardrobe memory and regression tests. Externalize legacy credentials and exclude private runtime state.

.env.example

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+# Copy to a private root-owned EnvironmentFile (0600). Never commit real values.
+# systemd does not expand $VAR or execute shell commands inside EnvironmentFile.
+PYTHONUNBUFFERED=1
+TZ=Asia/Shanghai
+DEEPSEEK_API_KEY=
+MODELSCOPE_API_KEY=
+AKAROS_MAIL_API_KEY=
+AKAROS_MAIL_ADDRESS=shirobana@akaros.si
+AKAROS_MAIL_FROM_NAME=白花
+KOMARI_API_BASE=https://status.example.com
+KOMARI_PASSWORD=
+PIXIV_CF_PASSWORD=
+BOT_SRS_CALLBACK_SECRET=
+# Optional: private file paths rather than inline secrets
+# MAIL_COM_TOKEN_FILE=/etc/shirobana-bot/mail-com-token
+# BOT_PROXY_CONFIG=/etc/shirobana-bot/proxies.json
+# OSS_SAVE_DIR=/mnt/oss/pixiv/images
+# NAPCAT_OSS_IMAGES_PATH=/mnt/oss/pixiv/images
+# BOT_LOG_UNIT=bot-utility.service
+
+# Only needed by the separately deployed Windows mail Web bridge.
+# mailWeb.py and com_backend.py are distinct programs: com_backend uses its
+# private com-private.json; these variables configure mailWeb.py.
+HMAIL_ADMIN_PASSWORD=
+MAIL_REGISTER_AUTH_CODE=
+MAIL_FLASK_SECRET_KEY=