docs(intern-22): speed benchmark multi-format (#360)

[CodingMinh]

Summary

• Chạy speed benchmark intern-22 trên corpus bench/sample10/, 36 file.
• Báo cáo bench/INTERN22_SPEED.md: bảng ms/file, ms/page + mục Phân tích intern-22.
• Harness nằm trong crates/cli/src/main.rs (cmd_speed, render_speed_report) — không có commands/speed.rs.

Given / When / Then

• Given: release CLI (cargo build --release -p fileconv-cli), PDFium + Tesseract 5.5 trên WSL.
• When: ./target/release/fileconv speed bench/sample10 bench/INTERN22_SPEED.md
• Then: 36/36 OK; summary theo định dạng; so sánh ≥2 format trong report.

Format comparison (ms/file TB)

Loại	ms/file	Observation
pptx	0.17	Nhanh nhất
xlsx	0.44	calamine
csv	2.45	parser thuần
docx	11.39	ZIP + XML
html	44.51	wiki-vn.html nặng
pdf	306.02	pdf-inspector + OCR trang cần

Regression

So với bench/REPORT_SAMPLE10_SPEED.md: thứ tự pdf ≫ html > docx giữ nguyên; chênh số tuyệt đối ~17–90% trên vài format (máy khác, không đổi code). Không regression do commit.

Lưu ý: make_sample10.sh thiếu PNG (gtts not installed) — không đo được image OCR lần này.

Closes #360

Test plan

• cargo build --release -p fileconv-cli
• bash bench/make_sample10.sh (partial — no images/audio)
• ./target/release/fileconv speed bench/sample10 bench/INTERN22_SPEED.md

[cursor]

PR Summary

Low Risk
Documentation-only benchmark report; no application or CLI code changes in the diff.

Overview
Adds bench/INTERN22_SPEED.md, the output of running fileconv speed on the bench/sample10/ corpus (36 files, all OK). The report includes per-file timings, per-format aggregates (ms/file, ms/page, KB/s), and an intern-22 (#360) analysis section.

The analysis ranks formats by average ms/file (pptx/xlsx fastest, pdf slowest at ~306 ms/file), explains why PDF lags CSV/HTML/DOCX, and compares totals to bench/REPORT_SAMPLE10_SPEED.md. It concludes format ordering is unchanged and absolute deltas are likely machine/WSL/corpus noise—not a code regression. Notes corpus lacked PNG/audio (gtts missing).

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