R5: fix architectural layering violations #274
Description
Epic: #268 | Phase: 4 — Architecture | Priority: P1 | Complexity: L
R5.1 — Move CliChannel to zeph-channels [M]
CliChannel defined in zeph-core/src/channel.rs but belongs in zeph-channels alongside TelegramChannel. Keep Channel trait in zeph-core.
R5.2 — Extract Embedder trait [L]
zeph-memory depends on zeph-llm for LlmProvider (embedding only). Extract minimal Embedder trait into zeph-core. Memory crate depends on trait, LLM crate implements it.
R5.3 — Update zeph-index Embedder bound [M]
After R5.2, replace LlmProvider bound with Embedder in zeph-index.
Blocked by: #270 (R1.1 LlmError)