Task #222 partial — unblock AB Legacy PCCC via cip-path workaround (5/5 stages)

Replaced the "ab_server PCCC upstream-broken" skip gate with the actual
root cause: libplctag's ab_server rejects empty CIP routing paths at the
unconnected-send layer before the PCCC dispatcher runs. Real SLC/
MicroLogix/PLC-5 hardware accepts empty paths (no backplane); ab_server
does not. With `/1,0` in place, N (Int16), F (Float32), and L (Int32)
file reads + writes round-trip cleanly across all three compose profiles.

## Fixture changes

- `AbLegacyServerFixture.cs`:
  - Drop `AB_LEGACY_TRUST_WIRE` env var + the reachable-but-untrusted
    skip branch. Fixture now only skips on TCP unreachability.
  - Add `AB_LEGACY_CIP_PATH` env var (default `1,0`) + expose `CipPath`
    property. Set `AB_LEGACY_CIP_PATH=` (empty) against real hardware.
  - Shorter skip messages on the `[AbLegacyFact]` / `[AbLegacyTheory]`
    attributes — one reason: endpoint not reachable.

- `AbLegacyReadSmokeTests.cs`:
  - Device URI built from `sim.CipPath` instead of hardcoded empty path.
  - New `AB_LEGACY_COMPOSE_PROFILE` env var filters the parametric
    theory to the running container's family. Only one container binds
    `:44818` at a time, so cross-family params would otherwise fail.
  - `Slc500_write_then_read_round_trip` skips cleanly when the running
    profile isn't `slc500`.

## E2E + seed + docs

- `scripts/e2e/test-ablegacy.ps1` — drop the `AB_LEGACY_TRUST_WIRE`
  skip gate; synopsis calls out the `/1,0` vs empty cip-path split
  between the Docker fixture and real hardware.
- `scripts/e2e/e2e-config.sample.json` — sample gateway flipped from
  the hardware placeholder (`192.168.1.10`) to the Docker fixture
  (`127.0.0.1/1,0`); comment rewritten.
- `scripts/e2e/README.md` — AB Legacy expected-matrix row goes from
  SKIP to PASS.
- `scripts/smoke/seed-ablegacy-smoke.sql` — default HostAddress points
  at the Docker fixture + header / footer text reflect the new state.
- `tests/.../Docker/README.md` — "Known limitations" section rewritten
  to describe the cip-path gate (not a dispatcher gap); env-var table
  picks up `AB_LEGACY_CIP_PATH` + `AB_LEGACY_COMPOSE_PROFILE`.
- `docs/drivers/AbLegacy-Test-Fixture.md` + `docs/drivers/README.md`
  + `docs/DriverClis.md` — flip status from blocked to functional;
  residual bit-file-write gap (B3:0/5 → 0x803D0000) documented.

## Residual gap

Bit-file writes (`B3:0/5` style) surface `0x803D0000` against
`ab_server --plc=SLC500`; bit reads work. Non-blocking for smoke
coverage — N/F/L round-trip is enough. Real hardware / RSEmulate 500
for bit-write fidelity. Documented in `Docker/README.md` §"Known
limitations" + the `AbLegacy-Test-Fixture.md` follow-ups list.

## Verified

- Full-solution build: 0 errors, 334 pre-existing warnings.
- Integration suite passes per-profile with
  `AB_LEGACY_COMPOSE_PROFILE=<slc500|micrologix|plc5>` + matching
  compose container up.
- All four non-hardware e2e scripts (Modbus / AB CIP / AB Legacy / S7)
  now 5/5 against the respective docker-compose fixtures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/drivers/README.md

@@ -44,7 +44,7 @@ Each driver has a dedicated fixture doc that lays out what the integration / uni
 - [AB CIP](AbServer-Test-Fixture.md) — Dockerized `ab_server` (multi-stage build from libplctag source); atomic-read smoke across 4 families; UDT / ALMD / family quirks unit-only
 - [Modbus](Modbus-Test-Fixture.md) — Dockerized `pymodbus` + per-family JSON profiles (4 compose profiles); best-covered driver, gaps are error-path-shaped
 - [Siemens S7](S7-Test-Fixture.md) — Dockerized `python-snap7` server; DB/MB read + write round-trip verified end-to-end on `:1102`
-- [AB Legacy](AbLegacy-Test-Fixture.md) — Docker scaffold via `ab_server` PCCC mode (task #224); wire-level round-trip currently blocked by ab_server's PCCC coverage gap, docs call out RSEmulate 500 + lab-rig resolution paths
+- [AB Legacy](AbLegacy-Test-Fixture.md) — Dockerized `ab_server` PCCC mode across SLC500 / MicroLogix / PLC-5 profiles (task #224); N/F/L-file round-trip verified end-to-end. `/1,0` cip-path required for the Docker fixture; real hardware uses empty. Residual gap: bit-file writes (`B3:0/5`) still surface BadState — real HW / RSEmulate 500 for those
 - [TwinCAT](TwinCAT-Test-Fixture.md) — XAR-VM integration scaffolding (task #221); three smoke tests skip when VM unreachable. Unit via `FakeTwinCATClient` with native-notification harness
 - [FOCAS](FOCAS-Test-Fixture.md) — no integration fixture, unit-only via `FakeFocasClient`; Tier C out-of-process isolation scoped but not shipped
 - [OPC UA Client](OpcUaClient-Test-Fixture.md) — no integration fixture, unit-only via mocked `Session`; loopback against this repo's own server is the obvious next step