feat: --stats per-file token breakdown; exact post-run token count (#21 P7)

[igorls]

Part of #21 (P7). New --stats[=N] flag (require_equals so it never swallows the next argument), render_stats unit-tested in-process, run_with_args stats test, binary tests in tests/test_stats.rs. The post-run 'Estimated tokens' now reads back the written file and counts it with the selected encoding (the >128K warning uses it too); stdout keeps the bytes/4 estimate since the document is gone. Adds a stats field to Args/ResolvedConfig (mechanical edits to Args literals in tests). One existing test fixture (100K+ warning) used a single repeated letter that tokenizes to a quarter of bytes/4; it now uses content with ~1 token per pair.

[Copilot]

🟡 Changes recommended

Stats can trigger an irrelevant overwrite prompt and can misreport budget boundaries due to divergent header accounting.

2 open findings

• Skip overwrite prompts for stats-only invocations · New
• Use exact rendered header token count for max-token decisions · New

What changed in this PR

Adds per-file token statistics and exact post-run token counting.

Changes:

• Adds --stats[=N] with budget-aware file breakdowns.
• Uses the selected tokenizer for post-run file counts.
• Adds unit, integration, documentation, and fixture updates.

File	Description
src/​cli.rs	Defines --stats.
src/​config_resolver.rs	Propagates stats configuration.
src/​lib.rs	Renders stats and exact token reports.
tests/​test_stats.rs	Tests stats and token reporting.
tests/​test_noninteractive_prompts.rs	Updates large-output fixture.
tests/​cli_integration.rs	Updates argument fixtures.
tests/​test_auto_diff.rs	Updates argument fixtures.
tests/​test_binary_file_autodiff.rs	Updates argument fixtures.
tests/​test_comprehensive_edge_cases.rs	Updates argument fixtures.
tests/​test_config_resolution.rs	Propagates stats in test resolution.
tests/​test_content_filter.rs	Updates argument fixtures.
tests/​test_cwd_independence.rs	Updates argument fixtures.
tests/​test_determinism.rs	Updates argument fixtures.
tests/​test_file_metadata.rs	Updates argument fixtures.
tests/​test_inclusion.rs	Updates argument fixtures.
tests/​test_parallel_memory.rs	Updates argument fixtures.
tests/​test_phase4_integration.rs	Updates argument fixtures.
benches/​context_bench.rs	Updates benchmark arguments.
README.md	Documents --stats.
SKILL.md	Adds stats usage guidance.
CHANGELOG.md	Records the feature.

🧠 Review effort: Balanced

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.