Epic: #1978

AnyChannel enum dispatch in zeph-channels/src/any.rs does NOT forward 4 Channel trait methods:

• send_thinking_chunk
• send_stop_hint
• send_usage
• send_tool_start

These fall through to default no-ops, meaning no channel routed through AnyChannel receives these events.

Fix: Add forwarding via dispatch_channel! macro for all 4 methods.

Location: crates/zeph-channels/src/any.rs

Acceptance Criteria:

• All 16 Channel trait methods forwarded in AnyChannel
• Compile-time check that new trait methods are not forgotten (exhaustive match or trait test)
• All tests pass

Complexity: Small | Effort: 30m
Ref: CHAN-01