feat(editor): vim-style search & replace in the query buffer

[killertux]

What

Adds vim-style search and replace to the query editor, plus version bump to 0.18.0.

:s substitute — :[range]s/pattern/replacement/flags

• Ranges: current line (:s/…), whole buffer (:%s/…), line addresses (:3,7s/…), ./$ addresses, and visual selection (:'<,'>s/…). Pressing : in Visual mode now pre-fills '<,'>.
• Flags: g (all matches per line), i (ignore case), c (interactive confirm).
• Patterns use the Rust regex crate. Replacement supports $1/${name} and the vim forms \1, & (whole match), \& (literal &). A literal $ is $$.
• Alternate separators (:s#a#b#), escaped separators (:s/a\/b/c/), and :s//new/ reusing the last pattern.
• Vim-faithful feedback: cursor lands on the last changed line, status reads N substitutions on M lines, and a missing match reports Pattern not found: <pat>.

Interactive confirm (c flag)

:%s/foo/bar/gc opens a bottom-bar prompt highlighting each match: y replace, n skip, a all, l last, q/Esc stop. Matches are scanned live so column shifts after each replacement stay correct.

/ search UX

Keeps edtui's built-in search engine but adds the missing feedback: the /pattern echoes in the bottom bar while typing, all matches highlight live, and a plain Esc in Normal mode clears them (:nohlsearch).

Undo

The entire substitution — including a full interactive confirm session — is a single u, via an edtui capture snapshot taken before mutation (pinned by a regression test).

Implementation

• New pure engine src/substitute.rs (parse/translate/resolve/apply, ~25 unit tests).
• Live-scan confirm state src/state/substitute_confirm.rs.
• Dispatch in src/action/substitute.rs; command hook in src/command.rs; key + bottom-bar wiring in src/event.rs / src/ui/bottom_bar.rs; :help section added.
• New regex dependency.

Testing

• cargo fmt --check, cargo clippy, and the full suite (655 tests) all pass.
• Smoke-tested in the running TUI: all range forms, the gc confirm walk, empty-pattern reuse, the not-found error, alternate separators, Visual-mode prefill + selection scoping, single-step undo, and invalid-regex errors.