OMNIS-36: Polish the TUI after the first reviews

[JtheGunner]

OMNIS-36

Polishes the TUI with the points deferred from the reviews of OMNIS-31 to OMNIS-34, plus a finding from manual testing of the options editor: the text cursor could not be seen or moved.

Changes

• Text fields: the filter and the option value editor keep a cursor (left/right, home/end, ctrl+a/e, delete), accept bracketed paste (cleaned of control characters) and show the real terminal cursor, also while a long value is scrolled.
• Cleaning: sanitize is now modedit.Clean; omnishell list uses it for table and JSON, and ModuleView.Unavailable and the filter header are cleaned too.
• Layout: status messages wrap over up to three lines (the real "install one of those shells first" message is now fully readable at 80 columns), "Terminal too small" is cut to the terminal width, wrapped detail lines get a hanging indent, and the Host line says an OS-only module can still be enabled but apply skips it.
• Plan screen: long lines and errors wrap and scroll, y/Enter only hand over while the plan is on screen, a is ignored (with a note) while an earlier plan is computed, and the footer says apply asks again.
• Robustness: an external SIGINT ends the UI quietly; after a successful write whose re-read fails, a toggle shows the written state, and the options screen locks its value keys (r reads again) and still counts the change.
• apply: prints "Nothing to apply: ..." when it finds nothing to do (also when run directly, not only after a hand-off).
• Docs and config: README, CLAUDE.md and CHANGELOG updated, tui --help has no line over 80 characters, .gitattributes protects the golden files from whitespace stripping.

Commits

• feat: move the cursor and paste in the TUI text fields
• fix: clean manifest text before it reaches the terminal
• fix: wrap long status messages and cap the too-small notice
• fix: indent wrapped detail lines under their value
• fix: wrap, scroll and guard the plan screen
• fix: keep the TUI truthful when a re-read fails after a write
• fix: say so when apply finds nothing to do after a TUI hand-off
• docs: describe the TUI polish and wrap the tui help text
• fix: count a written option after a failed re-read and explain the ignored plan key

Test plan

Run locally: go vet ./..., go test ./... -race, golangci-lint v2.13.2 (0 issues), all six release targets build, go.mod and go.sum unchanged. Driven in a pseudo-terminal with a throwaway HOME: the cursor is shown and moves with the left key.

For a reviewer, in a real terminal with a scratch HOME:

1. omnishell tui, o on fzf, Enter on default_opts: the cursor is visible, left/right/home/end move it, typing and pasting insert at the cursor.
2. / in the browser: move the cursor and paste into the filter.
3. Try to enable zshonly on a bash-only host: the full message is readable.
4. a on a long plan: lines wrap and scroll; do not confirm y unless you want apply to run.