feat(emacs): add skip-csi-sequence command

[maxlandon]

Implements the remaining command from #5: skip-csi-sequence (the GNU readline command name; issue text had it transposed as "csi-skip-sequence").

What it does

Terminals encode special keys (Home, End, function keys, modified arrows) as CSI sequences — ESC [ followed by parameter/intermediate bytes (0x20–0x3F) and a single final byte (0x40–0x7E). A key with no explicit binding would otherwise have its trailing bytes (15~, Z, 1;5D, …) self-inserted as stray characters.

skip-csi-sequence drains the remainder of such a sequence so unrecognized keys do nothing. Bound to \e[, it's the fallback for any CSI sequence no longer/exact binding claims; the dispatcher's longest-match means arrow keys (\e[A) etc. still win.

Note: it is not equivalent to zsh's self-insert-unmeta (as the issue's parenthetical suggested) — that inserts a meta-stripped key, whereas this discards an unrecognized sequence.

Scope

• Unbound by default, matching GNU readline (inputrc/bind.go already carries // skip-csi-sequence (not bound) in every keymap). Enable via inputrc: "\e[": skip-csi-sequence.
• No public API change — it's a keymap command, registered in standardCommands.
• No default-behavior change.

Testing

TestSkipCsiSequence covers params+final, bare final byte, modified-arrow params, stops-at-final-while-keeping-following-keys, and the empty no-op. Full suite, go vet, and golangci-lint clean.

Wiki (separate repo) documents both skip-csi-sequence and bracketed-paste-begin in Keymaps & Commands.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.33%. Comparing base (f79650a) to head (d4d431e).
⚠️ Report is 36 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   32.54%   38.33%   +5.79%     
==========================================
  Files          58       59       +1     
  Lines        9207     9516     +309     
==========================================
+ Hits         2996     3648     +652     
+ Misses       6173     5785     -388     
- Partials       38       83      +45     

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