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

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+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

profiles/sawtooth-gradient.yaml

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+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

profiles/sine-overunders.yaml

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+name: Sine over-unders
+description: >-
+  Warm-up ramp, then eight sinusoidal cycles oscillating either side of
+  threshold, then a cool-down. Power-channel, so the trainer holds the target
+  regardless of cadence.
+looping: false
+
+blocks:
+  # Ten-minute warm-up, 100 W rising to 200 W.
+  - type: ramp
+    channel: power
+    from: 100.0
+    to: 200.0
+    extent:
+      seconds: 600.0
+
+  # Eight two-minute cycles: 240 W mean, +/- 40 W.
+  - type: wave
+    channel: power
+    shape: sine
+    midpoint: 240.0
+    amplitude: 40.0
+    period:
+      seconds: 120.0
+    repeats: 8.0
+
+  # Five-minute cool-down.
+  - type: constant
+    channel: power
+    value: 120.0
+    extent:
+      seconds: 300.0

profiles/square-resistance.yaml

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+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