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/sawtooth-gradient.yaml

@@ -0,0 +1,29 @@
+name: Sawtooth gradient
+description: >-
+  Distance-based sawtooth on the gradient channel — the road tilts up gradually
+  then drops away sharply, repeatedly. Exercises virtual-gearing feel rather
+  than raw power, and is a good manual test of profile interpolation.
+looping: false
+
+blocks:
+  - type: constant
+    channel: gradient
+    value: 0.0
+    extent:
+      seconds: 300.0
+
+  # Ten 400 m teeth, ramping 0% to 8% then snapping back.
+  - type: wave
+    channel: gradient
+    shape: sawtooth
+    midpoint: 4.0
+    amplitude: 4.0
+    period:
+      metres: 400.0
+    repeats: 10.0
+
+  - type: constant
+    channel: gradient
+    value: 0.0
+    extent:
+      seconds: 300.0