feat(output): support table column labels in overlays

[samzong]

Summary

• Add output.default_columns and output.column_labels to command overlays.
• Compile table labels into runtime output hints while preserving JSON, YAML, and raw output.
• Support deep dot-separated fields, ordinary spaces, and hyphens while rejecting table control characters.

Verification

• go test ./pkg/runtime -run 'TestFormatOutput_(TableUsesNestedListPath|TableUsesConfiguredColumnLabels)$' -count=1
• go test ./internal/codegen/render -run 'TestRenderModule_AppliesOverlay|TestMergeOverlayModule_OutputColumns' -count=1
• go test ./internal/overlay -run TestLoadDir_ParsesExtendedFields -count=1
• make check
• go test -race ./...

Compatibility

• Generated CommandSpec literals may include the optional OutputHints.ColumnLabels field.
• runtime.SchemaVersion remains 11 because existing generated modules remain compatible.
• Catalog schema and JSON, YAML, and raw output are unchanged; only table rendering uses labels.
• CLI usage documentation and the overlay example are updated.

Checklist

• Tests or focused verification cover the changed surface.
• User-facing behavior changes are documented.
• Generated output under internal/generated/, .cache/, and ad-hoc skills/<cli-name>/ directories is not committed.
• Commits are signed off when this is ready to merge.

[codspeed-hq]

Merging this PR will improve performance by 16.06%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 10 improved benchmarks
✅ 11 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	large	2.1 ms	1.7 ms	+26.04%
⚡	table	796.9 µs	651.3 µs	+22.37%
⚡	yaml	5.4 ms	4.6 ms	+18.38%
⚡	small	193 µs	166.4 µs	+15.97%
⚡	BenchmarkFindCatalogCommand	8.7 µs	7.6 µs	+14.48%
⚡	large	2.4 ms	2.1 ms	+14.44%
⚡	large	1.6 ms	1.4 ms	+13.84%
⚡	json-small	255.9 µs	227.8 µs	+12.36%
⚡	small	142.6 µs	127.5 µs	+11.81%
⚡	BenchmarkCatalogJSON	3 ms	2.6 ms	+11.77%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing feat/table-column-overrides (61706d7) with main (c383c72)}