test(wl_replay): cover all replay handler bodies (20% → 79%) — G3 batch 3c

Adds 18 unit tests covering execute_approved_action and all 5 handler
bodies plus the precondition validation paths and the try/except wrapper.

New test classes:
- TestDispatchExceptionHandler — handler raising propagates as
  handler_exception (covers wrapper try/except at lines 116-126)
- TestRulePreconditionValidation — create_rule with existing rule →
  rule_exists; delete_rule with missing rule → rule_not_found
- TestCreateRuleHandler / TestDeleteRuleHandler / TestDeleteCsvHandler
  — happy + failure paths for the three pipeline-delegating handlers
- TestSaveCsvHandler — happy path with all mocks; write_csv exception;
  audit-post failure still returns success
- TestRevertCsvHandlerKnownBug — documents a discovered production bug
  (see "Known bug" note below)
- TestCreateCsvHandler — invalid name, file-exists, full happy path,
  mapping RMW OSError handled

Coverage: bin/wl_replay.py 20% → 79% (+59 percentage points). Tests:
716 → 734 (+18 added).

KNOWN BUG DISCOVERED (documented in TestRevertCsvHandlerKnownBug):
`_execute_replay_revert_csv` at line 226 calls `get_versions_dir()`
with NO arguments, but the function signature in bin/wl_versions.py
line 40 requires `csv_path: str`. This ALWAYS raises TypeError, which
is caught by the broad `except Exception` at line 309 and returns
{"error_type": "revert_failed"}. Lines 229-307 are effectively dead
code in production. Approving a revert_csv request through the queue
silently fails with a generic "missing 1 required positional
argument" error string.

The bug is NOT fixed in this commit — it is a behaviour change that
should ship in a dedicated fix commit with an E2E test. Two tests
in TestRevertCsvHandlerKnownBug pin the current (buggy) behaviour
so a future fix is observable as a test break.

Mock strategy: all domain-module imports (write_csv, snapshot_version,
post_audit_event, create_rule_pipeline, etc.) are patched on the
wl_replay module namespace because wl_replay imports them at module
top. The exception is read_version_manifest/get_versions_dir which
are imported INSIDE _execute_replay_revert_csv — for those we patch
the source module (wl_versions), matching the same pattern used in
test_versions.py G3 batch 3b.

No source code (bin/*) was modified. Pure test-addition commit.

Author: RelativisticJet