fix(cluster): apply AlphaFloor in dial calibration sweep

[devin-ai-integration]

Summary

computeDialCalibration swept raw alpha values without applying AlphaFloor, so breakpoints included mix changes at alphas the dial can never reach (floored slots hold at floor[i]), producing long dead zones on floored bundles (e.g. v0.73). The sweep now shares the flooring with applyDialAlpha via a new applyAlphaFloor(alpha, raw, floor) helper (alpha[i] = max(raw, floor[i]), nil floor disables), so breakpoints exclude unreachable low-alpha regions.

Tests: floored-bundle (v0.73) variants of the no-dead-zone and mid-dial-pricier distribution guards, direct applyAlphaFloor coverage, and breakpoint checks that no interior breakpoint falls below min(AlphaFloor) (committed bundle + heterogeneous-floor synthetic).

Adapted from #781 by @rohith500 (logic unchanged; comments reworked to match repo conventions).

Link to Devin session: https://app.devin.ai/sessions/75cb14caa09442c6a0ca9116059ed63f
Requested by: @steventohme

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