fix(sidebar): move the height floor onto the History section (review I1)

Review caught that min-h-56 on the middle wrapper did not deliver what its
comment claimed. The floor is shared with the Recent Matters block, which
cannot shrink - with a full 5-matter list Recent Matters (~220px) eats the
entire 224px floor and the History section resolves to ZERO height: empty
list, header flush against the bottom. That is the exact configuration the
pilot firm will QA.

Drop the floor from the wrapper (it now sizes to content inside the
scrollable column) and put min-h-48 on the History section, where it
actually protects the list. The row container is itself a scroll
container, so its automatic minimum size is 0 and the section still
resolves to a bounded height.

Re-measured in a corrected harness - hard config this time: full 5-matter
Recent Matters, firm-admin nav, and the logo row OUTSIDE the scroll
column as in the real code (the first harness wrongly nested it):

  viewport   main            min-h-56 wrapper   min-h-48 History
  796px      history 0px,    history 0px        history 192px,
             escapes card    (no escape)        rows 174px
  676px      history 0px,    history 0px        history 192px,
             escapes card    (no escape)        rows 174px
  1006px     history 60px,   history 60px       history 192px,
             rows 42px       rows 42px          rows 174px

Matches the reviewer's independent measurement (192/168; the 6px delta is
header line-height modelling). Accepted trade-off, as flagged: at ~1030px
with 5 recent matters the outer column becomes scrollable where today it
is not - scroll is acceptable, an empty history list is not, and the fix
buys 174px of rows against main's 42px at that height.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>