Add example profiles and noisy sample GPX

Four profiles exercising each waveform and channel; all verified to parse
against the Profile schema. Sample GPX has realistic GPS elevation noise so
the smoothing path (FR-5.2) is actually tested.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

profiles/hill-repeats.yaml

@@ -0,0 +1,19 @@
+name: Short hill repeats
+description: >-
+  Distance-based terrain loop: a flat approach, a steady climb, then a descent
+  to recover. Loops indefinitely, so ride it for as long as you can stand.
+looping: true
+
+blocks:
+  - type: segments
+    segments:
+      - distance_m: 500.0
+        gradient_pct: 0.0
+      - distance_m: 800.0
+        gradient_pct: 6.5
+      - distance_m: 200.0
+        gradient_pct: 9.0
+      - distance_m: 400.0
+        gradient_pct: -3.0
+      - distance_m: 300.0
+        gradient_pct: 0.0