journal: carried next steps carry their age; the carry is bounded and announces what it withheld

[laynepenney]

Ref #984 — closes at promotion.

What changes

The carry-forward retirement predicate stays exact (a near-miss never retires; a wrongly retired step is gone, a stale one is at least visible). What changes is what a reader can see:

• each carried step is stamped [carried since YYYY-MM-DD] with the date of the entry it was first written in; the stamp is preserved, never refreshed, on later carries; done matching ignores the stamp, so a carried step retires whether its text is listed bare or stamped
• at most 20 carried steps are kept on a new entry; the rest are withheld and a final [carry bound] N carried steps withheld; oldest since … line announces it; the marker is never itself carried, and action=pending skips it
• the write confirmation always prints Carry-forward: N carried, M retired by done, K withheld. (zeros included, so a filter that retired something never renders like one with nothing to do; this was Atlas r1's finding on v1) and, when anything is carried, how to retire a carried step: list its exact text under done
• merge_carried_forward_with_report returns the list plus a CarryReport; merge_carried_forward_next_steps remains as a back-compatible wrapper; the MCP and CLI write paths use the report form

Evidence (all runs with PYTHONPATH pinned to this checkout; import path printed)

• affected suites (test_cli, test_journal, test_resume, test_journal_collapse, test_server_resume): 223 passed
• full suite: 3140 passed, 10 failed; 9 of the 10 fail identically on an origin/dev base worktree (CrewAI and Google ADK adapters need an embedder / ADK install; one entry-point discovery), the tenth was a legacy expectation moved in this PR and now passes
• ruff 0.15.12 on the six touched files: 33 findings on origin/dev, 33 on this branch, delta zero, none on changed lines (an earlier draft of this body said 30/30; that count covered five files, before test_cli.py joined the change, and was caught in review)

Deliberately not done

The predicate is not loosened (substring or token overlap), per the issue's own caution. No schema change: the stamp lives in the step text so every existing reader renders the age with no code change.

Premium boundary: recall is OSS (journal storage and rendering); no boundary change.

Reviewers: r1 Atlas, r2 Sentinel.