feat(mail): mailforward write endpoints — add / update / delete

[chmmou]

Vertical-slice (per kasapi-cli-vertical-slice SKILL) for the mailforward write endpoints. Subset of #13.

KAS actions in scope

• add_mailforward
• update_mailforward
• delete_mailforward

Notes

• Fixtures already in testdata/mailforward/ (PR test: restructure KAS API fixtures into per-package folders #22).
• delete_mailforward is destructive — depends on the confirmation infrastructure in feat(cli): destructive-write confirmation infrastructure (--yes / interactive prompt) #109.
• Read counterpart get_mailforwards is already wired.

Acceptance

• SOAP request encoder + per-action mapping in internal/mailforward/ — PR feat(mail): mailforward write endpoints — add / update / delete #167 (write.go: Add/Update/Delete + AddParams/UpdateParams/DeleteParams, single-source-of-truth param builders; ErrUnexpectedReturnString contract sentinel).
• *Client write methods + per-package Caller interface tests — PR feat(mail): mailforward write endpoints — add / update / delete #167 (reuses the shared kasread.Caller; write_test.go covers success against the real fixtures, validation, the ReturnString!="TRUE" contract, error propagation, and a fault-fixture↔contract test).
• CLI subcommands wired + registered — PR feat(mail): mailforward write endpoints — add / update / delete #167. Wired under the existing mail forwards tree in internal/cli/mail.go (add/update/delete), not a separate internal/cli/mailforward.go as the issue text predated the consolidation of the forwards tree into mail.go; registered via the existing cli.NewMailCmd in cmd/kasapi-cli/main.go (no main.go change needed).
• make docs regenerated and committed — PR feat(mail): mailforward write endpoints — add / update / delete #167 (3 new + 4 updated docs/cli/ pages).
• CHANGELOG ### Added entry — PR feat(mail): mailforward write endpoints — add / update / delete #167.
• PR references this issue with Closes #<n> — PR feat(mail): mailforward write endpoints — add / update / delete #167 (Closes #115, merged 1b56d1a).

Status (codebase verified against main @ 1b56d1a, 2026-05-17)

Mail-forward write slice landed in PR #167 and merged to main via signed FF-push (61ff693..1b56d1a). delete and update are gated by the #109 confirmation prompt (update_mailforward replaces the full target list and is irreversible); add is reversible and not prompted. All three honour --dry-run (#132) and emit a #131 audit record, via the shared cli.runWriteE runner and the new non-gated cli.ResolveWrite. As the first concrete #13 write endpoint this also satisfied and closed the deferred end-to-end boxes of #109 / #131 / #132 (same commit).

Parent: #13

[chmmou]

Reconciled and closed by PR #167 (feat(mail): mailforward write endpoints, merged to main via signed FF-push 61ff693..1b56d1a). The mail-forward write slice is the first concrete #13 write endpoint and exercises this end-to-end through cli.runWriteE; all acceptance boxes are now checked. 6/6 CI gates green; branch deleted remote+local.