feat(memory): add secure user-owned memory store

[delkc]

Summary

Add the secure, user-owned foundation for Berd Memory.

• Store approved memory in readable ~/.me/me.md and ~/.me/topics/*.md files
• Respect the shared policy.json switch and deliver approved memory to supported agent sessions
• Publish a managed projection to ~/.agents/AGENTS.md without changing unrelated content
• Scope renderer writes to ~/.me, reject symlink/path escapes, and fail closed on unapproved external edits
• Share approved-content hashing and credential detection through the Rust memory core

Related issue

N/A. Bottom PR in the Memory stack.

Testing

• TypeScript typecheck, i18n, Biome, and design-system checks
• Memory preamble, publication, topic, policy, and credential tests
• Rust memory store and shared-core tests

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