v0.7.1: walk the ladder once ever — persistent learned modes, rule pins, same-boot iPXE recovery

Answers the operational question 'can a machine try all three boot
binaries in one go?' The protocol can't carry three NBPs in one cycle
(one boot file per DHCP round, the Secure-Boot refusal happens after
handoff with no error report, and the broken-NIC case specifically needs
the firmware itself to load builtin-driver iPXE — GRUB's network rides
the same broken firmware stack). What we CAN do is make the walk a
once-per-machine-ever event and give operators a way to skip it:

- Learned driver modes persist (<work_dir>/driver_modes.json). A MAC
  that reaches the Shim rung, or confirms an iPXE handoff at Builtin,
  is pinned to disk: immune to the 30-min TTL, reloaded at startup.
  The file only carries exceptions — a healthy fleet never writes it.
  Corrupt file starts empty (standard crash-cache policy).
- Boot rules gain an optional driver_mode pin (auto/firmware/builtin/
  shim), consulted by the DHCP proxy BEFORE the escalation ladder:
  'this OUI is a Secure Boot rack -> serve shim immediately' = zero
  failed cycles. Mode-only rules coexist with target rules (a pin
  doesn't shadow a later target match). Editor column on Hosts tab.
- grub.cfg now tries to chainload all-drivers iPXE before showing the
  signed menu: with SB off the chainload succeeds and the client gets
  the full iPXE feature set back in the SAME boot (self-healing for
  mis-escalations, and the handoff then pins the working mode); with
  SB on, shim's verifier refuses it inline — no reboot — and the
  signed menu appears.

DhcpProxyServer now takes the escalation table + rules store from main
(persistence path comes from the configured work dir).

Validation: clippy clean, fmt clean, 299 workspace tests green (+9:
persistence round-trip across restart, Shim pin survives TTL, learned
Builtin survives TTL, corrupt-file recovery, default-mode-never-
persisted, rule-pin matching incl. unknown-mode tolerance and
pin/target coexistence, GRUB chainload-before-menu ordering, API
round-trip of the driver_mode field).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

Cargo.toml

@@ -12,7 +12,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.7.0"
+version = "0.7.1"
 edition = "2021"
 rust-version = "1.95"
 license = "MIT OR Apache-2.0"