Add pomodoro, microbreaks, breathing guide, screen dimming, presentation mode, goals, multi-monitor, and activity manager

Major feature release (v0.1.3) adding 15 new features to the break timer:

Backend (Rust):
- Pomodoro cycle tracking with configurable short/long break pattern
- Microbreak scheduling (20-20-20 rule) with independent timer
- Screen dimming events with gradual opacity progression
- Presentation mode detection (fullscreen app deferral)
- Smart break detection (natural idle breaks counting toward goals)
- Daily goal tracking and streak milestone events
- Multi-monitor break overlay support
- Working hours enforcement with per-day schedules
- Weekly summary and natural break stats queries
- Config expanded to 71 validated fields

Frontend (Svelte):
- 6 new components: BreathingGuide, ActivityManager, BreakOverlay,
  MicrobreakOverlay, DimOverlay, Celebration
- Breathing guide with 5 patterns and animated pulsing halo
- Activity manager with favorites, custom activities, momentum scroll
- Confetti celebrations on milestones and goal completion
- Dashboard indicators (pomodoro/microbreak/goal) moved inside ring
- Settings reorganized into 18 logical cards
- Breathing pattern selector redesigned with timing descriptions
- Break activities expanded from 40 to 71 curated exercises
- Sound presets expanded from 4 to 8
- Stats view with weekly summary and natural break tracking

Also: version bump to 0.1.3, CHANGELOG, README and CLAUDE.md updates

src/lib/components/DimOverlay.svelte

@@ -0,0 +1,23 @@
+<script lang="ts">
+  import { onMount } from "svelte";
+  import { listen } from "@tauri-apps/api/event";
+
+  let opacity = $state(0);
+
+  onMount(async () => {
+    await listen<{ progress: number; maxOpacity: number }>("screen-dim-update", (event) => {
+      opacity = event.payload.progress * event.payload.maxOpacity;
+    });
+
+    // When break starts, this window gets destroyed by backend
+    await listen("break-started", () => {
+      opacity = 0;
+    });
+  });
+</script>
+
+<div
+  class="fixed inset-0 pointer-events-none"
+  style="background: rgba(0, 0, 0, {opacity}); transition: opacity 1s linear;"
+  aria-hidden="true"
+></div>