feat(api): reshape raw events into TimelineItem

GET /v1/events now returns the presentation form rather than raw
upstream payloads. The frontend stays dumb: it renders title /
subtitle / body segments and picks an icon from a small kebab-case
enum. Title and subtitle are arrays of {text} | {text, url} segments
so the UI can interleave plain copy with anchors without parsing.

New entities (in moments-entities):

  TimelineItem        — id, source, action, occurred_at, icon, title, subtitle, body
  TitleSegment        — Text | Link
  TimelineBody        — Markdown | Commits | Links
  CommitSummary       — sha, short_sha, message, url, author
  TimelineIcon        — kebab-case enum; UI falls back to Generic on unknowns

Reshape lives in moments-core::presentation, dispatched by source.
github.rs covers the event types observed on grenade's feed:
PushEvent, PullRequest{,Review,ReviewComment}Event, Issues{,Comment}Event,
Create/Delete/Fork/Watch/Release/CommitComment/PublicEvent.
Anything else falls back to a generic "<action> on <repo>" line.
Other sources (gitea, hg, bugzilla) currently use a stub fallback;
they get their own reshape modules in steps 5 and 6.

4 unit tests cover the load-bearing cases (push commit list, merged
PR icon swap, issue-comment markdown body, unknown-event fallback).

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

crates/moments-api/src/main.rs

@@ -9,9 +9,9 @@ use axum::{
 };
 use chrono::{DateTime, Utc};
 use clap::Parser;
-use moments_core::EventReader;
+use moments_core::{EventReader, reshape};
 use moments_data::PgStore;
-use moments_entities::{Event, EventQuery, Source, SourceSummary};
+use moments_entities::{EventQuery, Source, SourceSummary, TimelineItem};
 use serde::Deserialize;
 use tower_http::{cors::CorsLayer, trace::TraceLayer};
 use tracing::info;
@@ -83,7 +83,7 @@ struct EventsQueryParams {
 async fn list_events(
     State(state): State<AppState>,
     Query(params): Query<EventsQueryParams>,
-) -> Result<Json<Vec<Event>>, ApiError> {
+) -> Result<Json<Vec<TimelineItem>>, ApiError> {
     let sources = params
         .source
         .as_deref()
@@ -100,7 +100,8 @@ async fn list_events(
     };
 
     let events = state.store.list_events(&query).await.map_err(internal)?;
-    Ok(Json(events))
+    let items: Vec<TimelineItem> = events.iter().map(reshape).collect();
+    Ok(Json(items))
 }
 
 async fn list_sources(