feat(coverage): add whole-project scope to cj/coverage-report

Adds a fifth entry to the scope completing-read menu: "Whole project — all executable lines". Uses the existing cj/coverage-report flow, so the user still hits F7 and picks from the menu; the command dispatches based on the chosen scope.

Two new pure helpers back the scope:

- cj/--coverage-simplecov-executable-lines parses the simplecov JSON and returns every executable line per file (both hit lines and 0-hit lines, excluding null/non-executable entries). Symmetric with cj/--coverage-parse-simplecov, which returns only hit lines.
- cj/--coverage-format-summary renders intersect records as a per-file percentage summary sorted ascending by coverage (worst-covered first). Used instead of the line-detail format-report because an entire project's uncovered lines would be thousands of entries.

cj/--coverage-read-and-display now branches on scope: whole-project feeds executable-lines as the "changed" input to intersect; diff-aware scopes still shell git diff as before. cj/--coverage-render-to-buffer branches similarly to pick the format helper.

Tests cover the two new helpers: Normal (basic extraction, sorted output, percentages), Boundary (all-null coverage, multiple test-name keys unioned, empty records, not-tracked files excluded), and Error (missing file signals user-error).

Verified end-to-end on the current .coverage/simplecov.json: 2717 of 4559 lines covered across 44 files, sorted from keybindings.el at 0% up through high-coverage modules.

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