feat(navigation): label the tab bar

[bmc08gt]

Adds a name under each tab glyph, in tab order Scan, Chat, Wallet, You, per node 10642:1325, and titles the Chat screen "Chat" from the same string. The labels always show; the iOS bar's fold-on-scroll is left for a later change.

What changes

• Labels. String resources in :apps:flipcash:core, set in white and dimmed with the rest of the item when unselected. The design sets them in Demi 10 on a 12pt line (node 10599:65384). The theme has no 10sp token, so the name uses caption with its 18sp line height dropped, which keeps the text box tight under the glyph instead of adding a one-off style.
• Item and pill. The design's item is 86.5×50pt with 5pt above the glyph and below the name. Glyph and name share a column padded by staticGrid.x1 (5dp), and the selected pill takes the row's height, so it frames both.
• Bar inset. The design insets the bar 24pt from each screen edge. It was grid.x8, which is 40dp at the normal width class and left each item nearly square, so the pill read as a circle. It is now staticGrid.x5 (25dp).
• Selected pill. As on the iOS bar, the pill reaches past its item, 10dp (staticGrid.x2) on each side, into matching side padding in the bar. The extra width keeps a "99+" badge inside the pill's round ends.
• Glyphs and badge. Glyphs are 28dp to match the design, off the 5dp grid. The Chat tab's unread badge follows node 10599:65444: 17.5dp tall, starting 16dp into the glyph and rising 3.25dp above it, so the pill shows above the badge. Longer counts grow right from that start. The glyph's box is fixed to its size so "99+" can't pull the glyph off centre.
• Size on device. On a Seeker each item measures 85×54dp. The extra 4dp of height is caption's 12sp text box against the design's 12pt line.

Why no scroll fold

An earlier revision folded the labels away while a tab scrolled down. It resized the bar and its haze blur on every animation frame, and a scroll that kept folding and unfolding ran at a 19ms median frame against 14ms on code/cash on the same Seeker. It was dropped rather than tuned.