feat(routines): add Title 24 offset-2 high limit

[jscott3201]

Summary

• add the Zone 6 representative Title 24 differential dry-bulb specialization for climate zones 6, 8, and 9
• preserve the pinned donor graph and E3 golden artifacts byte-for-byte
• register the fourth AirEconomizerHighLimits scalar specialization and update catalog counts

Scope

Adds only G36-GEN-AEHL__title24-differential-offset-2 with TCut = TRet - 2 K. Coverage metadata, the offset-3 specialization, and E4/E5 claims remain unchanged.

Pinned revisions

• engine: e2ff2f84577d9be65a49e6cb5440c223f6126817
• donor: 41e997fd130c5e454446b40bcc3ba576429876b4
• source: a131864e4c4df22ebcd52bb8da439de0087ac365
• runtime content ID: cxf:fnv1a128:601ebab3b8983e44635e1766b7a2bcd8

Validation

• python3 tools/lint/svg_fitment.py
• python3 tools/lint/registry.py
• python3 -m unittest discover -s tools/lint/tests -v
• python3 tools/lint/routines.py --donor-root <checkout at DONOR_PIN>
• cargo test --manifest-path tools/verify/Cargo.toml
• cargo run --manifest-path tools/verify/Cargo.toml -- --routines
• cargo run --manifest-path tools/verify/Cargo.toml -- --all
• python3 -m unittest discover -s tools/dataset_harness/tests -v
• workflow dataset replay and result assertions
• python3 tools/book/generate.py twice
• mdbook build book
• git diff --check

All gates pass locally at head 2c0558e7975c553bad69e451ea936691710adde3.

[jscott3201]

Cycle 1 review result: PASS

Reviewed immutable target 8272193c1981d8c4ae215ee9c0836b21cc56d090...2c0558e7975c553bad69e451ea936691710adde3 with the holistic and dataflow review lenses.

• Blocker/major findings: none
• Deferred minor/nit findings: none
• Exact-head build and verify checks: successful
• Local full gates, donor parity, pinned content identity, and scope checks: passed

The PR is blocker/major-clean at the reviewed head.