Generalize Memory identity for multi-agent support

Generalize Memory identity to support non-Telegram agents.

Problem

Memory.hs and MemorySources.hs are tied to Telegram-specific identity:

• user_id is a Telegram user UUID
• chat_id is a Telegram chat ID (Int)
• MemorySources functions require these specific types

Solution

Introduce a generic MemoryIdentity type:

data MemoryIdentity = MemoryIdentity
  { miOwner :: Text    -- who owns this data (user, org, agent)
  , miContext :: Text  -- session/conversation context
  }

• Telegram: MemoryIdentity telegramUserId ("telegram:" <> show chatId)
• CLI: MemoryIdentity "ben" "cli:session-123"
• agentd: MemoryIdentity "system" ("agentd:" <> runId)

Changes

1. Add MemoryIdentity type to Memory.hs 2. Update MemorySources to accept MemoryIdentity 3. Update buildHydrationConfig signature 4. Update Telegram.hs to construct MemoryIdentity 5. Create memory.md skill for active memory use

Non-goals (for now)

• Schema migration (keep existing columns, just use them more flexibly)
• Provider abstraction (separate task t-500)