M3: Persistent memory and Claude provider

[bug-ops]

Goal

Conversations persist in SQLite across restarts. Claude available as a second LLM provider, selectable via config.

Scope

• SQLite conversation store (sqlx)
• History included in LLM context
• Claude API backend
• Config-based provider selection

Acceptance Criteria

• Conversation history survives restarts
• History visible in LLM context (configurable limit)
• Claude works: ZEPH_LLM_PROVIDER=claude cargo run
• Both providers pass same functional tests

Child Issues

• Implement SQLite conversation store with sqlx #17 Implement SQLite conversation store with sqlx
• Wire SQLite memory into agent loop #18 Wire SQLite memory into agent loop
• Implement ClaudeProvider for Anthropic API #19 Implement ClaudeProvider for Anthropic API
• Add config-based LLM provider selection #20 Add config-based LLM provider selection

Depends On

#3 (M2)