[ADD] tui: interactive terminal UI for resolving duplicates

The tool could only act on duplicates non-interactively or through a
line-oriented per-group prompt. Add a full-screen terminal UI (--tui) for
browsing and resolving them visually.

The UI is a two-pane master/detail view: a list of duplicate groups and,
for the selected group, its files with per-file deletion marks. Files can
be marked individually or in bulk by a keep-strategy (newest/oldest/first/
last/shortest/shallowest, reused from the resolver) applied to the current
group or to all groups at once. A footer tracks how many files are marked
and how much space would be reclaimed. Deletion is gated behind an explicit
confirmation, a group always keeps at least one file, and the highlighted
file can be opened in the system default application.

The design keeps the interaction logic pure and independently testable: an
App model translates an abstract key event into an outcome, so navigation,
marking, strategy application, and post-deletion model updates are all unit
tested without a terminal. Rendering (ratatui) and the destructive file I/O
live in the event loop, which restores the terminal on both normal exit and
panic so a crash never leaves it broken. --tui is mutually exclusive with
--keep and --interactive.

Cargo.toml

@@ -26,8 +26,10 @@ globwalk = "0.9.1"
 gxhash = { version = "3.4.1", default-features = false }
 indicatif = { version = "0.18.0", features = ["rayon"] }
 memmap2 = "0.9.7"
+open = "5.4.0"
 pathdiff = "0.2.1"
 prettytable-rs = "0.10.0"
+ratatui = "0.30.2"
 rayon = "1.6.1"
 unicode-segmentation = "1.12.0"