docs: clarify current engineering scope and preserved evidence

[AlbertXXuu]

Problem and behavior

The current README and charter made outside adoption a prerequisite for further engineering, while completed phase plans could still be read as active assignments. The documentation now defines the next milestone through the existing authorized workflow, fresh-environment verification, readable failures and independent evidence. Historical plans keep their original contents with a current-scope notice.

This changes 16 documentation files only. Automatic generation, saved time and production-support claims still require their own evidence; frozen case artifacts and runtime code are unchanged.

Validation

• git diff --check, changed-document local-link audit and introduced-secret/path scan: passed.
• node scripts/verify-brand.mjs: passed.
• Reused unchanged stage-one results: DrawDB saved 20 expected pre-fix failures / 20 post-fix passes; Safe Unfollow evidence verification passed; a bounded extraction of the existing real CLI fixture completed a 2+2 differential and rejected 19 corrupt evidence bundles.
• The comprehensive local CLI test did not pass: the sandbox restricted Windows process inspection, and the user-environment rerun reached its existing 180-second total limit. Later exception/cancellation branches are not claimed as locally verified. The repository's complete Node 22/24 checks run in this PR's CI.

No new package, release, public case or model execution is introduced.