Adds IncidentTimeline.vue — a pure SVG time-axis component rendered inside the
incident detail drawer when entries are present:
- Horizontal strip scaled to incident window (preserveAspectRatio=none)
- Event ticks colored by severity, height proportional to severity level
- 50-bin density shading shows burst periods as blue bands
- Gap markers (dashed lines) for silence > 10% of window or > 60s
- Hover tooltip showing nearest entry's severity, time, and truncated text
- Click-to-scroll: clicking a tick highlights and scrolls to its entry in the list below
- Legend showing only severity levels present in the incident
Also fixes a pre-existing bug: get_incident_endpoint and both build_bundle callers
were passing INCIDENTS_DB_PATH to get_incident_entries/build_bundle, causing all
incident entry lookups to silently search the empty incidents DB instead of the
main log DB. This made all incident detail views show "No log entries found".
Closes: #57
