ci.yml: pin ci-result's needs, decouple breg-tutorial from Evidence changes, inventory the composition job, raise the breg-contracts budget

[jeremi]

1. Nothing pins ci-result's needs list. Conditional jobs such as rust-tests, the four *-contracts jobs, identifiers and docs-archives gate only through rust-result or docs-required, and docs-required itself is absent from ci-result's needs. A test in .github/scripts (or release/scripts/check-gates-inventory.py) should hold the list.
2. registry-mint links registry-evidence, so an Evidence change selects breg-tutorial through the mint reverse dependency. The classifier should say whether that is intended.
3. check-gates-inventory.py carries no entry for the breg-evidence-composition job; removing the job would not fail the inventory.
4. breg-contracts has timeout-minutes: 20 and runs within a minute of it. Decision pending: raise the budget (30 would match breg-evidence-composition) or shorten the journeys step, which is the largest share.

Run	Duration
main, typical	17 min 45 s
PR #865 heads, typical	19 min 06 s to 19 min 29 s
PR #865 fifth head, attempt 1	cancelled by the job timeout at 20 min 11 s
PR #865 fifth head, rerun	16 min 49 s

Origin: review of PR #865.

[jeremi]

Item 4: PR #883 (open) splits breg-contracts into a three-lane matrix (contracts, postgres, immediate-actions), which is the "shorten the journeys step" option; the 30-minute budget from PR #851 stays as the safety margin. Items 1 to 3 are not touched by #883 as far as its diff shows (ci-result needs, the Evidence-to-breg-tutorial routing, and the breg-evidence-composition inventory entry).

[jeremi]

Triage: item 4 is done on main (breg-contracts has timeout-minutes: 30). Items 1 to 3 are deferred until PR #899 merges, since that PR rewrites ci.yml and the classifier tests these items would touch.