chore: scaffold moments workspace

Cargo workspace with five crates per architecture conventions:

- moments-entities: Source enum, Event, EventQuery, SourceSummary
- moments-core:     EventReader / EventWriter ports
- moments-data:     PgStore (sqlx postgres adapter) + 0001_init.sql
- moments-api:      axum binary; /v1/{healthz,events,sources}
- moments-worker:   skeleton; pollers land in step 2

Sources committed-to for ingestion: github, gitea, hg, bugzilla.
Workstation events explicitly retired (not deferred).

Build + clippy clean. sqlx queries use the runtime API for now;
will switch to compile-time-checked macros + .sqlx offline cache
once magrathea has the moments_{ro,rw} roles and database created.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/moments-core/src/lib.rs

@@ -0,0 +1,21 @@
+use async_trait::async_trait;
+use moments_entities::{Event, EventQuery, SourceSummary};
+
+#[derive(Debug, thiserror::Error)]
+pub enum StoreError {
+    #[error("database error: {0}")]
+    Database(String),
+}
+
+/// Read-side port consumed by `moments-api`.
+#[async_trait]
+pub trait EventReader: Send + Sync {
+    async fn list_events(&self, query: &EventQuery) -> Result<Vec<Event>, StoreError>;
+    async fn source_summaries(&self) -> Result<Vec<SourceSummary>, StoreError>;
+}
+
+/// Write-side port consumed by `moments-worker`. Idempotent upserts on `id`.
+#[async_trait]
+pub trait EventWriter: Send + Sync {
+    async fn upsert_events(&self, events: &[Event]) -> Result<usize, StoreError>;
+}