Retire the agent-commit Bats suites where Go covers them #858

Problem

The Bats suites tests/skills/agent-commit/workflow.bats and base-merge.bats still test unattended-mode and base-merge shell behavior that agentrepo commit --unattended now owns, so they duplicate the Go tests and must shrink to the cases that still need a real shell or the fallback.

Part of #322, within #588. Child 09 in #322's Children list. Deletes test cases only; no skill source or generated skill changes.

Acceptance criteria

1. AC1: Given every case in tests/skills/agent-commit/workflow.bats and tests/skills/agent-commit/base-merge.bats, when the pull request is read, then each case is marked deleted with the Go test that covers it, or kept as a wrapper, fallback or real-shell case with the reason, and no case is unaccounted for.
2. AC2: Given the merged change, then every case marked deleted is absent and every kept case passes.
3. AC3: Given the Go tests named for the deleted cases, when CI runs, then they pass on macOS, Linux and Windows.
4. AC4: Given the generated skills, then nothing changes and mise run check-generated-skills passes.

Scope and non-goals

Scope: tests/skills/agent-commit/workflow.bats and tests/skills/agent-commit/base-merge.bats and a case ledger in the pull request.

Non-goal: changing any wrapper, fallback or generated output. Non-goal: removing the frozen fallback before the N-2 window closes. Out of scope: Bats suites for other skills.

Approach

Meet AC1 to AC4. List the cases, match each to a Go test from children 01 to 06, delete the duplicates and keep the wrapper and fallback cases. The mechanism is the implementer's choice.

Dependencies

Blocked by: #855 and #856.

Size

S. One pull request, deletions only. Estimated code SLOC counted with scc rules on the case files: 546 lines of code at most, under the 800 limit; none of it is in a generated path.

Verify plan

• AC1: the ledger in the pull request lists every case in tests/skills/agent-commit/workflow.bats and tests/skills/agent-commit/base-merge.bats.
• AC2: the Bats run for the remaining cases passes and the diff shows only ledger-marked deletions.
• AC3: the CI matrix jobs for the named Go tests.
• AC4: mise run check-generated-skills passes with no diff.
• Definition of done: D1 each AC is verified at the merged head, with the commands and results cited in the pull request's Verification. D2 an independent review approves the exact merged head, and every finding has a recorded disposition. D3 required checks pass with no gate loosened. D4 the leak scans the repository specifies are clean, and every post made for this work passes the per-post leak review before it is posted. D5 every commit is signed. D6 the documentation matches the change or the Verification says why there is no impact. D7 every commit has an Assisted-by trailer and the pull request has the provenance:agent-assisted label. D8 the pull request stays within the size limits. D9 follow-ups are filed as issues and listed under Related. D10 the merge closes the issue through a closing reference, the board shows Done, and the final Status: comment names the merge commit.

Risks

Deleting a case whose Go equivalent is weaker loses coverage; the ledger names the covering test and the review checks it. Undo: revert the change, which restores the cases.

Operator authority

None.