Problem

When compiled with --features postgres, the following files fail to compile because they hardcode SqliteStore::new(&config.memory.sqlite_path):

• src/commands/skill.rs
• src/commands/memory.rs
• src/commands/sessions.rs
• src/runner.rs
• src/acp.rs
• src/scheduler.rs

These are CLI subcommands (sessions, memory, skill) and internal services that directly construct the SQLite store.

Root Cause

Phase 1/2 debt: SqliteStore was introduced as the only concrete store implementation. When postgres feature is active, SqliteStore does not exist — callers must use a different API surface.

Expected Behavior

All CLI subcommands and services should compile and function correctly under both --features sqlite (default) and --features postgres builds.

Acceptance Criteria

• Each affected call site is either gated behind #[cfg(feature = "sqlite")] with a stub error for postgres, or migrated to use zeph_db::DbPool generics
• cargo check --workspace --no-default-features --features postgres,bundled-skills,scheduler,guardrail passes
• Existing sqlite tests unaffected

Context

Discovered during Phase 3 DevEx implementation (PR for db-abstraction-phase3). The zeph db migrate CLI subcommand was implemented successfully; other subcommands are blocked by this issue.