feat: markdown memory system — Hope learns from conversations

- agent/memory_mcp.py: MCP server with memory_recall, memory_save, memory_list
  tools backed by .md files in /memory (simple keyword matching for v1)
- memory/ dir bind-mounted into container, persists across rebuilds,
  easily backed up via git
- System prompt instructs Hope to recall on past references and save
  personal info/preferences naturally without announcing it
- Dockerfile: copy memory_mcp.py; compose: ./memory:/memory volume

memory/README.md

@@ -0,0 +1,28 @@
+# Hope's Memory
+
+Persistent memory for the voice assistant, stored as plain markdown files.
+This directory is bind-mounted into the container at `/memory`, so memories
+survive rebuilds and are backed up via git.
+
+## Format
+
+Each file is one topic, named after a slugified version of the topic
+(e.g. `user-preferences.md`, `birthday.md`). Content is freeform markdown
+notes. When Hope saves something, it appends a timestamped section:
+
+```markdown
+# User preferences
+
+## 2026-08-22 14:30 UTC
+
+Prefers to be called Shane. Works on the voice assistant project.
+
+## 2026-08-23 09:15 UTC
+
+Likes dark roast coffee, no sugar.
+```
+
+- `#` heading = the topic (written once when the file is created)
+- `## <timestamp>` headings = individual notes, appended over time
+- The MCP server (`agent/memory_mcp.py`) reads and appends these files;
+  you can also edit them by hand — Hope will pick up changes on next recall.