Refactor template rendering with Renderer interface for testability

Introduce a Renderer interface to abstract template rendering, enabling
tests to use MockRenderer instead of requiring real template files.

Changes:
- Add renderer.go with Renderer interface, TemplateRenderer, and MockRenderer
- Update Handler struct to use Renderer instead of *template.Template
- Update HTMLResponse() to accept Renderer interface
- Replace all h.templates.ExecuteTemplate() calls with h.renderer.Render()
- Update all tests to use MockRenderer, removing template file dependencies

This eliminates 15+ tests that previously skipped with "Templates not
available" and improves test isolation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/internal/handlers/timeline.go b/internal/handlers/timeline.go
index fa5bcec..29b156a 100644
--- a/internal/handlers/timeline.go
+++ b/internal/handlers/timeline.go
@@ -109,7 +109,7 @@ func (h *Handler) HandleTimeline(w http.ResponseWriter, r *http.Request) {
 		data.TomorrowHours = append(data.TomorrowHours, h)
 	}
 
-	HTMLResponse(w, h.templates, "timeline-tab", data)
+	HTMLResponse(w, h.renderer, "timeline-tab", data)
 }
 
 // calcCalendarBounds returns start/end hours for calendar view based on timed events.