Auto Doc Index — Derived Indexes from Frontmatter

Replaces hand-maintained index tables in README.md with auto-generated tables derived from structured frontmatter in individual doc files.

Why This Matters — Real Evidence

In a real project with 13 ADR files, comparing hand-maintained index vs auto-generated index revealed 8 discrepancies (62% error rate):

Issue Type	Example	Count
Title truncated	"activate none" vs actual "activate none by default"	2
Status fabricated	Index said "Decided" but file said "Accepted"	3
Date invented	Index showed "2026-01-28" but file had no Date field	1
Metadata lost	"(revised 2026-01-28)" stripped from status	1
Case "normalized"	`decided` silently changed to `Decided`	4

These aren't hypothetical risks — they were already present and invisible