[AZ-348] C3.5 ConditionalRefiner Protocol + factory + PassthroughRefiner

Defines the public `ConditionalRefiner` Protocol (PEP 544
@runtime_checkable, two methods: `refine_if_needed` +
`was_invoked`), extends `MatchResult` in-place with two
default-valued refinement fields (`refinement_label`,
`refinement_added_latency_ms`), defines the `RefinerError` family
(`RefinerBackboneError`, `RefinerConfigError`), and ships the
trivial `PassthroughRefiner` reference impl.

Both refiner strategies are linked unconditionally — no
`BUILD_REFINER_*` flag (NOT ADR-002 territory). Runtime selection
only per ADR-001. `PassthroughRefiner` returns the input
`MatchResult` by reference (bit-identical correspondences per
contract INV-5) and always reports `was_invoked() is False`.

Documentation: renames `module-layout.md` `c3_5_adhop` Public API
symbol from `AdHoPRefinementStrategy` to `ConditionalRefiner`
(AC-14) so the doc agrees with `description.md` and the contract.

AC-9 (single-thread binding) deferred to AZ-270 runtime-root
composition, mirroring AZ-336 / AZ-342 / AZ-344 Risk-4 precedent.
AC-7 for the `"adhop"` strategy stops at `ModuleNotFoundError`
because the AdHoP backbone is owned by AZ-349. All other ACs +
NFRs covered by 36 new conformance tests.

Architectural note: `PassthroughRefiner.inference_runtime` is
typed as `object` because the L3→L3 import ban
(`test_az270_compose_root`) forbids c3_5_adhop from importing
c7_inference; the runtime-root factory narrows the type at
construction time.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/_autodev_state.md

@@ -8,7 +8,7 @@ status: in_progress
 sub_step:
   phase: 2
   name: detect-progress
-  detail: "batch 24 in flight (per-task commits): AZ-336 done, AZ-342 done, AZ-344 done; next AZ-348"
+  detail: "batch 24 complete (AZ-336, AZ-342, AZ-344, AZ-348 per-task commits); ready to plan batch 25"
 retry_count: 0
 cycle: 1
 tracker: jira