v0.15.2 — ast_search ranking + dead-code --json empty contract

User-driven QA pass exercising every MCP tool + CLI subcommand surfaced two bugs whose contract violations were silent — both regressions guard against recurrence.

Fixes

• src/storage/queries.rs — get_nodes_with_files_by_filters (the SQL backing ast_search / ast-search) ordered by f.path ASC only, so the LIMIT clause silently truncated alphabetically-late files (src/storage/queries.rs itself, with 54 Result-returning fns) out of the top-N. New ordering is caller_count DESC, path ASC, line ASC so high-value symbols surface first regardless of file path.
• src/cli.rs:2655 — dead-code --json returned only stderr (no stdout) when all results were filtered by --ignore, breaking JSON consumers piping stdout. Now emits [] to stdout before the human stderr message, matching the established empty-result contract used by search / grep / callgraph / show / trace / overview.

New regression tests

• test_get_nodes_with_files_by_filters_ranks_by_caller_count (src/storage/queries.rs) — alphabetically-first low-caller fn must not outrank alphabetically-last high-caller fn at any LIMIT.
• test_cli_json_empty_dead_code (tests/cli_e2e.rs) — stdout must be [] and stderr must still surface "No dead code" when --ignore filters all results.

371 tests pass (was 369). Clippy 1.95 clean on both feature combos.

Full Changelog: v0.15.1...v0.15.2