feat: wire the cdd CLI (cdd, init, scan, version)

[hammadmajid]

What

Wires internal/cli to github.com/spf13/cobra: the root cdd command
(bare behaves as pick), pick [query], init <shell>, scan,
version, plus cobra's own help and completion commands. Flags
--help/-h and --version/-V (the latter prints the same output as
cdd version).

• pick loads config, opens History at its default path, and resolves the
  query via jump.Resolve + picker.Run, printing only the chosen
  Project's absolute path (plus newline) to stdout. A cancelled Picker
  exits 130 silently; any other error exits 1 with a stderr message. When
  stdout is a terminal, a stderr hint suggests installing the Wrapper via
  cdd init <shell> | source.
• init requires exactly one shell argument (fish, bash, zsh),
  otherwise exits 2 listing them. The Wrapper's pass-through list is
  derived from the cobra command tree (every command name except pick),
  so help and completion forward without hand maintenance.
• scan prints Seeded N Visits across M Projects and exits 0.
• version formats version/commit/date (same var names the scaffold
  and .goreleaser.yaml already reference via ldflags), falling back to
  cdd dev (dev) for local builds.
• Usage errors (unknown command/flag, wrong argument count, unsupported
  shell) exit 2; runtime errors exit 1 with a stderr message; a cancelled
  Picker exits 130 with no message.

internal/cli.Run(args, stdout, stderr) int is exported alongside
Execute() so tests drive the command tree in-process with cobra's
SetArgs and captured buffers, rather than exec'ing a built binary.

Testing

go build ./... && go vet ./... && go test ./... all pass. Table-driven
tests in internal/cli/cli_test.go cover version formatting and its
flag aliases, unknown command/flag exit codes, init's usage errors and
tree-derived passthrough list, pick/scan arg-count usage errors, and
help output.

Closes #21

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