style(tiles): bigger tile header buttons, the app header's icon size

Owner feedback: the tile header's ⋯ ⤢ + × read as tiny next to the
session name. The buttons inherited the header's 12px font. They are now
26px click targets (min-width, so a wider glyph still fits) with a 16px
glyph, the same as the app header's own icon buttons (.btn-icon-header);
the thin ellipsis and cross get 19px so all four read at one visual
size. The header grows from 24 to 28px to hold them, the inline rename
input to 22px. Checked live at DSF 1 on a dark (daylight-blue) and a
light (paper-gray) skin, focused and unfocused tiles, and a zoomed tile.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/tile-grid-plan.md

@@ -29,6 +29,9 @@ or settled a question the spec left open. The invariants as built are in
   B too), and a refresh clears the screen at its turn in the queue, so a waiting tile keeps
   its last frame.
 - **4009 lands on the Attach overlay**, and 4003/4004/4010 remove the tile.
+- **Tile header buttons are 26px targets with 16 to 19px glyphs** (owner feedback: the
+  first build's 12px glyphs read as tiny next to the name), the size of the app header's own
+  icon buttons; the header grew from 24 to 28px to hold them.
 - **The Tiles button opens the grid at once** (owner decision 8): a click (and
   `Ctrl+Shift+G`, the same `toggleTileGrid`) opens `tileGridOpenSet` (constants.js): the
   grid this tab last had, else an open split's two sessions, else the open sessions in tab