Sleep: stop the stage strip clipping into a row of circles (#36)

[ryanbr]

What #36 reported

On Android the sleep-hero stage graphic renders as a single row of disconnected circles (WHOOP 5.0, on-device staging) instead of a continuous stage strip.

Root cause

HypnogramWithAxis floored each segment to a min width (minSegW = h, 34dp) and advanced x by that floored width. Two things then break on a fragmented night (a WHOOP 5.0 metadata-only sync produces many short approximate segments):

1. Overflow / clipping — the floored widths sum past the canvas, so x runs off-screen and the tail clips. Only the first ~w/h segments (≈ the ~13 circles in the screenshot) stay visible; the rest of the night is drawn off-canvas.
2. Circles — each segment was drawn as an h-wide round-capped line, so any sub-h segment renders as a full h-diameter circle rather than a block.

Together: a disconnected row of circles on one line.

The fix (minimal — keeps the single strip)

• Floor every segment, then if the floored total overflows the canvas, scale them all to fit — the strip stays a continuous bar for the whole night instead of clipping the tail.
• Draw rounded rects (not round-capped lines) advancing by the same width they're drawn, so x can never exceed the canvas and a narrow segment reads as a thin block, not a circle.
• Proportions of normal-width segments are unchanged; the onset · midpoint · wake axis is untouched.

~20 lines in one function, no analytics change, no new composables.

Notes

• This is a genuinely data-poor night ("No movement detail", metadata-only sync), so the stages stay approximate — the strip is now correct and legible, not more precise.
• Chose the minimal single-strip fix over porting the iOS multi-lane (per-stage rows) layout; the multi-lane remains a possible later enhancement if we want "phases on separate lines."
• Android-only; compiles clean (compileFullReleaseKotlin).

Fixes #36.