feat(observability): emit EventBus events from HTTP write paths

[barrygfox]

Description

Wires the EventBus into the six HTTP write-path chokepoints that were previously silent. This is a pure observability improvement — it does not change any write behaviour, recall semantics, data model, or API contract.

Why proposed

Only MCP tool handlers emit EventBus events. Every HTTP fast path — /observe, /remember (sync and async), AutoCapture decisions, and the pending materializer drain — was silent. As a result, the dashboard health pane showed events_last_24h: 0, and the event stream stayed empty regardless of daemon traffic, making it impossible to distinguish a healthy, busy daemon from a stuck one.

Changes

infra/event_bus.py — four new event types registered (3 lines):

Type	When
memory.observed	/observe accepted content into the debounce buffer
memory.captured	AutoCapture matched a buffered observation
memory.dropped	AutoCapture rejected a buffered observation
memory.queued	/remember accepted content into pending.db (async path)

memory.stored already exists and is reused for the sync /remember and materializer paths.

server/unified_daemon.py — one new helper, six callsites:

• _emit_event(): mirrors mcp.shared.emit_event but tags source_protocol="http" so the dashboard can distinguish HTTP traffic from MCP tool calls. Best-effort — never raises, logs at DEBUG on failure.
• Wired into ObserveBuffer.enqueue, ObserveBuffer._flush (both capture and drop branches), POST /remember sync path, POST /remember async path, and materializer drain (source_agent="materializer").

tests/test_server/test_http_eventbus_emissions.py — 10 new tests:

• New event types present in VALID_EVENT_TYPES
• _emit_event never raises on bus error
• _emit_event tags source_protocol="http"
• ObserveBuffer.enqueue emits memory.observed
• Duplicate content does not emit a second memory.observed
• _flush emits memory.captured on AutoCapture match
• _flush emits memory.dropped on AutoCapture miss

What does not change

• No write path is altered
• No API response shape is changed
• No new dependencies
• Existing tests unaffected (388 pass on main after this change)