Re-port v2-grammar phases E/F-H/I/J onto upstream extern API

[hyperpolymath]

The 10-commit v2-grammar work on local main was superseded by a different, more-complete extern API merged upstream. main is now synced; the full lineage is preserved on pushed branch wip/v2-grammar-2026-05-16.

Scope: re-implement the genuinely-net-new phases — E (annotations + tuple destructuring), F/G/H (implicit-in, abstract extern types, Unit/Bytes), I (cross-module/import_resolver), J (bridge.eph + hypatia-port) — onto the upstream Extern { abi, items, span } + cross-module-registry API. Phase D already landed (#78). hello.eph is v2-only and dropped.

Ref branch: wip/v2-grammar-2026-05-16. Companion to hyperpolymath/standards#66.

[hyperpolymath]

Reopened. #80 carries major + requirements-target, so per the estate joint-close rule it must NOT auto-close on PR merge — it closes only on explicit joint-close agreement.

#80 was auto-closed when PR #83 merged even though that PR's body/title and the final squash commit message were corrected to Refs #80 (no closing keyword). Cause: the PR's original Closes #80 text created a persistent GitHub issue↔PR development link; editing the body afterwards does not sever that link, so GitHub closed the issue on merge regardless of the corrected text. Lesson: the closing keyword must never be committed in the first place for requirements-target issues — a later edit cannot undo the link.

Implementation status: the re-port (phases E/F-H/I/J) is fully merged via PR #83 (squash 7b1cd76), full suite green. This issue stays OPEN pending explicit joint-close agreement and will be mirrored to the "Awaiting joint close" board column.

[hyperpolymath]

Jointly closed by explicit user agreement (2026-05-17). Per the requirements-target joint-close rule, the user has explicitly agreed to close #80: the v2-grammar re-port (phases E/F-H/I/J onto the upstream extern API) landed via PR #83 (squash 7b1cd76, full suite green), and the spec for this issue is satisfied. Board mirror: hyperpolymath project #36 "Requirements-target / Joint close" → moved from "Awaiting joint close" to "Jointly closed".