docs: simplify rules benchmark table

[kvlonge]

Why

The five-column Rules benchmark table overflowed the documentation content area and partially hid the final edit result behind horizontal scrolling. Its "First Rules run" label was also less direct than the compile terminology used elsewhere.

Changes

• transpose the Rules benchmark table from five columns to three
• move compile scenarios into rows so all values remain visible
• rename the first scenario to "First compile (no cache)"
• use "Unchanged compile" consistently in the table and surrounding prose

Verification

• validated docs.json
• git diff --check
• public-repository hygiene scan
• manually checked table dimensions and retained values