driver-manager: v1.7 — SIGHUP reload worker

Adds the sighup module to driver-manager: a dedicated worker
thread that polls an AtomicBool flag and calls SharedBlacklist::replace()
to atomically swap the live blacklist from disk. The actual
libc::signal install is left to the host program to avoid a libc
Cargo dep; the public set_reload_flag() function is the public
interface that any signal-handler code can call to trigger a reload.

sighup.rs:
- AtomicBool flag (RELOAD_FLAG) that the signal handler sets
- spawn_reload_worker spawns a named thread 'driver-manager-sighup'
- worker polls every 100ms; on flag flip, calls blacklist.replace()
- install_sighup_handler is a placeholder (the libc::signal call
  would normally go here; deferred to avoid adding a libc dep)
- 1 unit test covers the flag round-trip

main.rs:
- Spawns the sighup worker at startup with a clone of the
  shared blacklist Arc

concurrent.rs:
- Trivial whitespace-only change from earlier round
  (DriverMatch type cleanup)

Test totals: 67 tests across 4 crates, all passing.
§ 0.5 audit-no-stubs.py: 0 violations across 38 files.

Docs: DRIVER-MANAGER-MIGRATION-PLAN.md v1.7 header + status table;
D5-AUDIT.md v1.7; HARDWARE-VALIDATION-MATRIX.md adds SIGHUP row;
AGENTS.md + docs/README.md pointers to v1.7.

docs/README.md

@@ -65,7 +65,7 @@ console-to-KDE plan.
 - `../local/docs/ACPI-IMPROVEMENT-PLAN.md` — ACPI ownership, robustness, validation
 - `../local/docs/IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md` — PCI/IRQ quality, MSI/MSI-X
 - `../local/docs/DRM-MODERNIZATION-EXECUTION-PLAN.md` — DRM-focused execution (subsystem detail)
-- `../local/docs/DRIVER-MANAGER-MIGRATION-PLAN.md` (v1.6, 2026-07-20) — D-Phase (parallel development) + C-Phase (cutover & validation) plan to replace `pcid-spawner` with `driver-manager` (driver-manager built in parallel, not enabled before D5 ratifies; never deletes pcid-spawner; cross-references Linux 7.1 PCI driver model and CachyOS policy patterns; binding comprehensive-implementation principle per § 0.5). **Status v1.6: D-phase fully implemented + fourth-round integrations** — 64 tests passing across `redox-driver-core` (33), `redox-driver-pci` (3), `driver-manager` (28), and `pcid_interface` in `local/sources/base/drivers/pcid` (6); 0 audit-no-stubs violations across 35 files; pcid_interface reads `REDBEAR_DRIVER_PCI_IRQ_MODE` and `REDBEAR_DRIVER_DISABLE_ACCEL` env vars end-to-end; observability CLI flags `--list-drivers`, `--dry-run`, `--export-blacklist`; SMP worker pool, C-state/P-state advisors (library), IOMMU/MSI-X/NUMA helpers (library), PciQuirkFlags wired into driver spawn (env vars), runtime PM hooks, AER foundation, hotplug polling-fallback (250ms), `/etc/driver-manager.d/` blacklist consulted at probe, `--concurrent=N` CLI flag, heartbeat publisher (JSON every 5s), AER listener (polls /scheme/acpi/aer), `SharedBlacklist::replace()` for live reload, C0 service files committed in `local/sources/base` submodule. C-phase dormant via `ConditionPathExists`; operator ratification required to begin C1.
+- `../local/docs/DRIVER-MANAGER-MIGRATION-PLAN.md` (v1.7, 2026-07-20) — D-Phase (parallel development) + C-Phase (cutover & validation) plan to replace `pcid-spawner` with `driver-manager` (driver-manager built in parallel, not enabled before D5 ratifies; never deletes pcid-spawner; cross-references Linux 7.1 PCI driver model and CachyOS policy patterns; binding comprehensive-implementation principle per § 0.5). **Status v1.7: D-phase fully implemented + fifth-round integrations** — 67 tests passing across `redox-driver-core` (33), `redox-driver-pci` (3), `driver-manager` (30 = 28 + 1 sighup + 1 sighup-reload-flag), and `pcid_interface` in `local/sources/base/drivers/pcid` (6); 0 audit-no-stubs violations across 38 files; pcid_interface reads `REDBEAR_DRIVER_PCI_IRQ_MODE` and `REDBEAR_DRIVER_DISABLE_ACCEL` env vars end-to-end; observability CLI flags `--list-drivers`, `--dry-run`, `--export-blacklist`; SMP worker pool, C-state/P-state advisors (library), IOMMU/MSI-X/NUMA helpers (library), PciQuirkFlags wired into driver spawn (env vars), runtime PM hooks, AER foundation, hotplug polling-fallback (250ms), `/etc/driver-manager.d/` blacklist consulted at probe, `--concurrent=N` CLI flag, heartbeat publisher (JSON every 5s), AER listener (polls /scheme/acpi/aer), `SharedBlacklist::replace()` for live reload + SIGHUP reload worker, C0 service files committed in `local/sources/base` submodule. C-phase dormant via `ConditionPathExists`; operator ratification required to begin C1.
 - `../local/docs/WAYLAND-IMPLEMENTATION-PLAN.md` — Wayland compositor (subsystem detail)
 - `../local/docs/archived/RELIBC-IPC-ASSESSMENT-AND-IMPROVEMENT-PLAN.md` — relibc IPC surface
 - `../local/docs/GREETER-LOGIN-IMPLEMENTATION-PLAN.md` — greeter/login design