docs: close C09A bounded PREVRANDAO milestone

[tanka420]

Summary

• record C09A-E5 closeout evidence and merged E1-E4 delivery commits
• move C09 and C09A execution plans from active to completed
• document the final parser/package boundary, supported Solidity/Foundry evidence, unsupported surfaces, and compatibility-shell limitation
• update the roadmap and rule-development backlog so C09/C09A are complete and C10 is the next sequenced engineering milestone

Why

C09A-E4 is merged on main, but the repository governance documents still describe C09A as planned/pending. E5 closes that documentation drift without changing runtime behavior.

Developer impact

• no production code, public rule behavior, package manifest, lockfile, schema, scoring, reporter, CLI, preset, or FindingV2 change
• inventory remains 19 known / 16 default / 7 wallet / 4 canonical
• both PREVRANDAO public IDs remain default-critical, non-canonical temporary compatibility shells
• C10 becomes the next sequenced engineering milestone after this closeout

Recorded implementation evidence

• E1 / PR C09A-E1: add private Solidity source analysis #63 / merge d829278f26669f6190a516cb3c0efed9aca7f49c
• E2 / PR feat(arcready): complete C09A-E2 bounded flow routing #65 / merge 5d368d7ac0d75a00c9d6dfb65496304040a738f7
• E3 / PR feat(arcready): compose Foundry PREVRANDAO eligibility #68 / merge a4d3a5cb5ea6eb92fd18f84c01e4c2c61ac54903
• E4 / PR feat(arcready): migrate PREVRANDAO compatibility shells #67 / merge bc0b00b88b295cfaa10f4b976b852229a5ffab8d

E4 recorded corepack pnpm verify:full passing, 41 package test files / 2,683 tests passing, 5/5 workflow tests passing, build/lint/package smoke passing, and independent review at 0 blocker / 0 major / 0 minor.

E5 validation required before merge

• current-head GitHub CI
• Repository Verification
• ArcReady Action Smoke
• ArcReady Example
• documentation/format and clean-diff gates
• final independent review with 0 blocker / 0 major / 0 minor

Scope

Documentation/governance only. Exact branch diff contains only C09/C09A plans, E5 closeout evidence, roadmap, and backlog files.