fix: fold text that has no spaces instead of cutting it off at the pane

[hidekingerz]

Summary

A Japanese paragraph, or any run of text without spaces such as a long URL, was cut off at the right edge of the pane instead of being folded, and once folded, a run that followed a space was moved to the next row whole, leaving a nearly empty row before it. Word wrapping (reflow/wordwrap, used by glamour and by mado itself) breaks only at spaces and hyphens.

• internal/ui/wrap.go: mado folds text itself. wrapText breaks a row at a space where one will do, between any two East Asian characters (Japanese has no spaces to offer), and inside a word only when the word alone is wider than the row. Wide characters count as two columns, escape sequences take none and stay whole, and closing marks such as 。 」 stay with the character before them while 「 （ stay with the one after (行頭・行末禁則, minimal).
• hardWrapLines folds glamour's already laid-out output the same way, keeping a paragraph's margin on the rows it continues on; glamour now renders with word wrap off (WithWordWrap(0)), which also stops it padding rows to the width.
• Tabs are expanded to the columns a terminal draws them at before folding; trailing spaces (glamour pads table cells) are kept only where they fit; an escape sequence inside a highlighted word stays in the word instead of becoming a break.
• Used everywhere text is folded: reader view, source view, line numbers (continuation rows keep the blank gutter) and the search jump's row count.
• New direct dependency on github.com/mattn/go-runewidth, already in the module graph; reflow is no longer used directly.

Test plan

• gofmt -l ., go vet ./..., TMPDIR=/tmp go test -race ./... clean
• New tests: reader and source view fold a spaceless sentence within the pane with no text lost; the row before a Japanese run is filled rather than left short; Latin words stay whole and an overlong word is split; escape sequences survive; no row starts with 。 or 、; line numbers number a folded line once; the search jump's row matches where the line is rendered; hardWrapLines keeps every line once and keeps an indent set behind escape sequences; mermaid diagrams still fit at the exact width and fall back one column narrower
• Probed headings, quotes, nested and ordered lists, inline styling, links, tables, code blocks, emoji, full- and half-width forms, Hangul and Chinese, spaceless URLs and kinsoku marks: no row wider than the pane, no text lost, no row starting with a closing mark
• tmux: README bullets, a paragraph starting with 「, mixed English/Japanese, a table, a rule and an English paragraph, in reader, source and numbered modes

🤖 Generated with Claude Code

https://claude.ai/code/session_01KUYF9hXeZFML1s8r3i2RVX