Add README, Docker packaging, and workspace templates

Docker build verified locally (docker build -t volcanic-secretary .
succeeded on this machine). Step 6's manual end-to-end checklist
against a real Telegram bot was not run in this environment (no bot
token or owner id available); the checklist is kept in the README's
Tests section for the owner to run before relying on this in
production.

Claude-Session: https://claude.ai/code/session_01JtuZTCMW9TyogEmBgGf8JT

workspace/AGENTS.md

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+# Workspace
+
+This directory belongs to Volcanic Secretary, a personal assistant reached over Telegram.
+
+- MEMORY.md: durable facts about the owner. Keep it current.
+- scripts/: scripts for scheduled jobs.
+- inbox/: files the owner sent.
+- .secretary/: runtime state. Do not edit by hand.
+
+Standing instructions for the assistant go below this line.

workspace/MEMORY.md

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+# Memory
+
+Durable facts the assistant should remember. The assistant edits this file itself.
+
+## Owner
+
+## Preferences
+
+## Ongoing