feat(app): Home, the Library and the studyset sheets laid out as before

Home: plain cards on the surface, 16 dp apart, the goal first and the
Pomodoro timer after it in a new dashboard. The streak chip sits centred
in the app bar, and its sheet shows the days inside a big flame and the
week as marks over the weekdays' initials, with a word on today in a box.
The week names its day as "Thursday, Oct 8" and its days carry no
tooltip. The heatmap scrolls its weekdays with the weeks, outlines the
days to come, and names a day's activities with its date. The goal card
has a ring of 5 dp, a check once met and a pencil, and its sheet saves
across its width with Remove goal below. Arranging puts an eye on each
widget's corner and lifts the one picked up, with a tap the hand feels;
with every widget hidden, Customise brings arranging back. The stepper
moves to core, where the goal's sheet takes it too.

Library: the counts line includes files (PDFs); Refresh in the app bar
and pulling the list down sync now; a list that can't be read offers
Retry, which reads it again; the star keeps its square corners.

Studyset sheet: "Title *", the secondary title explained behind a
question mark, Inherit as a box beside the colour, and the description
in up to three lines with a chevron. Move sheet: round marks, the
studyset itself marked as current, the top level only while it is
inside another, archived studysets last under their heading, the
destination named in the footer, and a new studyset to move into, made
only once the move is.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_en_US.arb

@@ -3,7 +3,7 @@
 
   "studysetSheetColor": "Color",
   "colorPickerLabel": "Color: {color}",
-  "studysetSheetInheritColor": "Same color as the studyset it is in",
   "tagSheetColor": "Color",
-  "formatAlignCenter": "Center"
+  "formatAlignCenter": "Center",
+  "homeCustomise": "Customize"
 }