The TUI has had instant fuzzy search since v0.1. The CLI has been blind:
once a project has >20 tasks, finding one means scrolling `ls` output
manually. This adds the same search affordance to scripts and one-shots.

Implementation:
  - Reuses internal/util/fuzzy (sahilm/fuzzy), same scoring as the TUI
  - Default index: title + #tags + notes
  - --title-only restricts to titles
  - Filter: undone by default, --done | --all
  - --limit N caps results
  - --format plain/table/json (table reuses #6 renderer)
  - --json shortcut preserved, mutually exclusive with --format
  - Empty result: "no matches for <q>" in text, "[]" in JSON

Examples:
  tsk search milk
  tsk search "fix login" --limit 5
  tsk search dev --all
  tsk search docs --json | jq

Tests: 10 cases — title match, tag match, --title-only, done filter,
--all, --limit, --json non-empty, --json empty array, empty query
rejection, table format. All green with -race.