Add word wrap toggle for diff pane

[umputun]

Summary

• w key toggles word wrap in the diff pane — long lines wrap at the pane boundary with ↪ continuation markers instead of requiring horizontal scroll
• --wrap CLI flag and config file option to start with wrap enabled
• ↩ mode icon in status line when wrap is active (alongside ▼ collapsed and ◉ filter)
• Horizontal scroll (←/→) disabled when wrap is active, scrollX reset to 0
• Cursor/viewport math updated to account for multi-row wrapped lines
• Wrapping works in both expanded and collapsed diff modes
• Help overlay updated with w keybinding

[Copilot]

Pull request overview

Adds a word-wrap mode to the diff pane so long lines wrap at the viewport boundary (with ↪ continuation markers) instead of requiring horizontal scrolling, controllable via w and a new --wrap option.

Changes:

• Introduces wrapMode (configurable via CLI/env/config) and a w key toggle that resets horizontal scroll and re-syncs the viewport.
• Implements wrapped diff rendering (expanded + collapsed modes) with continuation markers and disables horizontal scroll while wrapping.
• Updates cursor/viewport math for wrapped visual rows and extends tests + documentation accordingly.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
ui/model.go	Adds wrapMode, config wiring, w toggle, horizontal scroll handler routing, status icon, and help text update.
ui/model_test.go	Adds extensive coverage for wrap config, icons, rendering, wrapping math, toggle behavior, scroll blocking, and help text.
ui/diffview.go	Implements core wrapping logic (wrapContent, wrapped rendering, line counting) and disables horizontal scroll during wrap.
ui/collapsed.go	Applies wrapping behavior to collapsed-mode add/modify lines and delete-only placeholders; shares placeholder text logic for math sync.
ui/collapsed_test.go	Adds collapsed-mode wrap rendering tests (markers, gutters, cursor placement, placeholder behavior).
ui/annotate.go	Updates cursorViewportY to account for wrapped visual rows and wrapped delete-only placeholders.
cmd/revdiff/main.go	Adds --wrap flag/env/config integration and wires it into ui.ModelConfig.
cmd/revdiff/main_test.go	Adds argument parsing coverage for --wrap via flag/env/config.
README.md	Documents wrap mode and the --wrap flag and keybinding.
docs/plans/completed/20260402-word-wrap.md	Marks implementation plan tasks as completed.
CLAUDE.md	Documents the wrap-mode rendering flow and cursor math adjustments.
.claude-plugin/skills/revdiff/references/usage.md	Adds w keybinding to usage reference.
.claude-plugin/skills/revdiff/references/config.md	Adds --wrap/REVDIFF_WRAP to config reference.

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