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/square-resistance.yaml

@@ -0,0 +1,28 @@
+name: Square-wave resistance intervals
+description: >-
+  Raw resistance-channel intervals, bypassing the physics model entirely.
+  Thirty seconds hard, thirty seconds easy, twenty times. Useful for
+  characterising the trainer's resistance curve by feel.
+looping: false
+
+blocks:
+  - type: constant
+    channel: resistance
+    value: 20.0
+    extent:
+      seconds: 300.0
+
+  - type: wave
+    channel: resistance
+    shape: square
+    midpoint: 45.0
+    amplitude: 25.0
+    period:
+      seconds: 60.0
+    repeats: 20.0
+
+  - type: constant
+    channel: resistance
+    value: 15.0
+    extent:
+      seconds: 300.0