docs: record CSRG-U6 as the active unit

[novelKR]

Records CodeSpace's CSRG-U6 as the active unit in DevGuard's ledger. It is bookkeeping, the same kind of change as #28 and #30, and is not part of U6's definition of done.

Why

The owner directed CSRG-U6 to start on 2026-10-12. Its predecessor is on CodeSpace main: CSRG-U5 merged as novelKR/CodeSpace#92 (0c21a7f), recorded here by #31, and governed PTY executions have been observed before the reap since novelKR/CodeSpace#93 and novelKR/CodeSpace#95 (181a020), recorded by #32. CodeSpace main is now 7024f74 and still links this repository at 6e7e065; its post-merge CI is green: CI run 38233097644 and documentation run 38233098609. The ledger still records U6 as not-started.

Changes

File	Change
milestones.json	CSRG-U6 is active, the value #28 and #30 gave U4 and U5 when they started. units.as_of is 2026-10-12. CS-RG stays in-progress, qualification not-run
docs/milestones.md	The CS-RG row and the dated note under the suspension notice say U6 is the active unit
AGENTS.md	The dated current-state note says U6 is active
docs/planning/README.md, docs/ko/planning/README.md	The dated current-state note says U6 is active
docs/planning/milestones/CS-RG.md, docs/ko/planning/milestones/CS-RG.md	The dated current-state note says U6 is the active unit; its sentence on PTY observation is unchanged

Korean counterparts reviewed; planning-readme and planning-milestones-cs-rg hashes recorded with scripts/check_docs.py record.

What does not change

• CS-RG is not marked implemented or qualified. U6 is not recorded as merged and its qualification is not claimed: both wait for U6's evidence and the owner's exact-head approval.
• The suspension of the CSRG-C00–C09 plan stays in force, and no historical text is rewritten: each change is the existing dated note or the living status row.
• No product code, contract, design revision, pin, dependency, CI policy or test changes. The DG-1 qualified release stays 0.1.0-5daee5d-b3fa569e. As the owner chose on 2026-10-09 and 2026-10-12, a new release built from 6e7e065 is to replace it on the qualification host before U6's qualification; that release is not SLO-qualified until it is measured and promoted, and recording it is a separate change.

Verification

At 8fca59c, based on main at 152a2cf:

• python3 scripts/ci_plan.py --base origin/main --head HEAD: profile affected, 8 normative paths, stages whitespace, source-contract and documentation, no Rust.
• python3 scripts/validate.py --stages whitespace,source-contract,documentation --diff-base origin/main: all three passed.
• python3 scripts/check_docs.py: passed, 18 reviewed pairs, 48 work units, 25 logical PR groups.
• python3 -m unittest discover -s scripts -p 'test_ci_*.py': 95 tests passed.

Rollback

Revert the merge (git revert -m 1 <merge commit>). The ledger then reports U6 as not-started again, which would be inaccurate while U6 is under way.