fix(ui): move Compose back, drop the bar below the header, size its icons

Three corrections from looking at the built bar.

Compose returns to the main toolbar. The split this was built to, "about a
message" against "about the list", does not survive contact: what matters is
what the action NEEDS. Reply and Forward are meaningless without a message on
display, while Compose needs none and is disabled only when no account can
send. So the pane's bar holds exactly the two actions that depend on what it
is showing, and Compose sits with the window-wide ones.

The bar moves below the subject and details rows, directly above the web
view. At the top of the pane it read as window chrome rather than as
belonging to the message. The transient notice bars stay above it: they
explain the message rather than offer an action on it.

Its icons were the style's own default, 16px, which is tiny beside a 32px
toolbar. They are now 7/8 of toolbar_icon_size, which is the 28 the user
asked for at their 32, derived rather than hardcoded so the relation holds
if that key changes. The test asserts the relation as well as the value,
since a bare 28 would stop meaning anything the moment the key moved.

m_headerLabel gains an object name so the placement test can find the row it
must sit below.

1 files changed, 4 insertions, 4 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index cd3c419..da2156c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,7 +23,7 @@ point at which they are stable.
   reply follows what the message being answered used.
 - Drafts autosave to the account's `drafts` folder as ordinary Maildir files,
   so mbsync carries them to the server and another client can pick one up.
-- **A button bar over the message pane.** Compose, Reply and Forward sit
+- **A button bar over the message pane.** Reply and Forward sit directly
   above the message, with Toggle HTML at the right end. Forward had been
   reachable only from the Message menu.
 - A reply opens with the cursor on a blank line above the quote, and with the
@@ -48,9 +48,9 @@ point at which they are stable.
 
 ### Changed
 
-- The main toolbar keeps only the actions that act on the list or the
-  selection (Sync, Archive, Delete, Mark all read, Undo). Compose and Reply
-  move to the new message-pane bar, where Forward joins them.
+- The main toolbar keeps the actions that need no particular message
+  (Compose, Sync, Archive, Delete, Mark all read, Undo). Reply moves to the
+  new message-pane bar, where Forward joins it.
 
 ### Fixed