feat(minimap): draw the drawn pen across the archive (#91)

[mrcsin]

Problem

The minimap was a navigation strip with no data on it, and its window marker left the strip once the chart followed live data past the extent read at start (#91): the marker's left edge was not clamped, and the strip's right bound stayed at the startup extent.

What changed

• MinimapGeometry.MarkerSpan keeps the marker inside the strip at any zoom.
• The right bound is the later of the extent's last sample and ChartNavigationController.NewestSample, which the navigation raises on every write, sticky or not.
• MinimapBandFeed reads the drawn pen's band over the whole extent at the layer LayerForWidth(span, previous, 250) picks, on start, an extent reload, a drawn-pen change and clamp(span / 1000, 2 s, 60 s) after each read lands. A read for a pen no longer drawn is dropped; OutageReport reports the first failure of an outage and logs repeats, for the band and the extent re-read alike.
• MinimapGeometry.BandFigures turns the envelope into one figure per non-NaN run (finite values only, a flat pen at mid-height, a lone column 2 px wide); MinimapBand draws them in the pen's colour.
• The line through the middle of the strip is gone; the end labels sit in a row under the strip (the window's minimap row takes the view's own height), and hovering shows a 1 px line with its time to the minute.
• trend-interaction.md, charting.md, data-integration.md, ui-theme.md, bench.md, testing-strategy.md, TM-4 and CLAUDE.md follow the code; the plan moves to docs/plans/completed/.

Verification

• dotnet build SemiPlot.slnx: 0 warnings. Unit 1668/1668 under --blame-hang.
• AWindowPastTheExtent_KeepsItsMarkerInsideTheStrip and ANewerSampleThanTheExtent_MovesTheRightBoundAndItsLabel failed by assertion against the code before their fixes; TheMinimapRow_ShowsTheWholeLabelRowUnderTheStrip fails with the old Height="36".
• Manual run on the demo stand: the band and its gaps, a pen switch, a recolour, hiding the drawn pen, a 5-minute live follow, deep zoom at both ends, drag navigation, re-reads without jumps, the label row and the hover.

Closes #91

Per-task commits before collapse

9a78c94 docs(plans): record the label row and hover run
ff4dc5d refactor(minimap): address hover smells and comments
a8e13f9 fix(minimap): address label row review findings
de4fe94 docs(minimap): document the label row and the hover
66d5fea feat(minimap): show the time under the pointer
6b95339 feat(minimap): label the strip's ends under it
8a7d47b docs(plans): add the minimap label row and hover
d9cb8aa docs(plans): record the minimap-overview run
2d7504f refactor(minimap): drop restating comments
2384475 refactor(minimap): address smells findings
ed9df90 fix(minimap): address review findings
087e52a docs(minimap): describe the band, bounds and marker
9ace485 docs(plans): record the minimap acceptance run
4e0ed47 feat(minimap): draw the band on the strip
c83a577 feat(minimap): read the drawn pen's band
1a28c89 feat(minimap): shape the band in core
7de132c fix(minimap): move the right bound with the newest sample
02caa09 fix(minimap): keep the window marker inside the strip
73a1bd8 docs(plans): add minimap overview plan

https://claude.ai/code/session_01PfZJa7neMMKPzycFR6iuhD