Add a timeline page grouping photos by day

New /timeline/ page renders photos grouped into consecutive same-day
runs (ISO date heading plus per-day count), reusing the square grid.
groupByDay collapses the newest-first photo list; the page is not
paginated. Linked from the profile header.

CLAUDE.md

@@ -47,6 +47,7 @@ Missing sidecar → filename as caption, today as date. Photos sort newest first
 - Manjari for Malayalam text (bio line), via `-ml-family`
 - 3-column square grid → 2-column on mobile, 60 photos per page (`/`, `/page/2/`, …)
 - Single photo page with sidebar and newer/older navigation
+- Timeline page (`/timeline/`) groups photos by calendar day: one ISO date heading (`2026-06-14`) + count per day, then the same square grid. Linked from the profile header; `groupByDay` in `generator.go` collapses the newest-first photo list into consecutive same-day runs, so it is not paginated.
 
 ### Photo page navigation
 
@@ -130,6 +131,7 @@ nix build          # succeeds
 | `watcher.go` | fsnotify watcher with 500ms debounce |
 | `assets.go` | `//go:embed` for templates and static |
 | `templates/photo.html` | Single photo page, neighbour links and prefetch |
+| `templates/timeline.html` | Timeline page, photos grouped by day |
 | `static/photo-nav.js` | Arrow-key and swipe navigation |
 | `module.nix` | NixOS module (systemd service, tmpfiles, nginx vhost) |
 | `flake.nix` | `buildGoModule` package + devShell + nixosModules |