feat(timeline): stop two months back, and give the bars room

Two changes to how the board reads.

The window was drawn from the earliest start, so one long-running event — a
standing login campaign can have been going half a year — bought months of
empty calendar that nobody scrolls back through and that pushed every other
bar off to the right. It now floors at two months, a patch cycle and a half:
far enough that a running event's start is usually still on the board, past
the point where the answer changes what anyone does today. A bar older than
the board keeps its faded left edge rather than being redrawn as though it
started there.

The bars themselves were 28px with 4px between them, which read as a stack of
hairlines rather than a schedule. They are 36px now, with more padding, more
air between events, and more between lanes.

`boardWindow` comes out of the component while it is being changed: it
decides what a reader can and cannot see, which is worth a test rather than a
rendering.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/PRD.md

@@ -80,6 +80,12 @@ calendar on screen, and nothing left saying which day, whose game, or which even
 six-week bar starts weeks off-screen, so a name that rides off with its own start date leaves a
 coloured rectangle behind.
 
+**The board draws at most two months of past.** A standing login campaign can have been running for
+half a year, and drawing from the earliest start bought months of empty calendar that nobody scrolls
+back through and that pushed every other bar off to the right. An event older than the board keeps
+its faded left edge rather than being redrawn as though it started at the edge — the same honesty
+the frayed right edge carries for an unannounced end.
+
 **F2 — Ends-soonest list.**
 A flat list of all *currently running* events sorted ascending by end date, with a relative
 countdown ("ends in 2 days", "ends in 4 hours"). Under 24 hours, the row is emphasized. This is the