review: iteration-2 fixes (fragment assertion, evidence paths, hardening)

- build-kernel.sh fragment assertion: survives a missing trailing newline
  (the read footgun, reproduced) and treats an absent symbol on a disable
  line as FATAL, symmetric with the enable arm.
- fetch-kernel-tarball.sh checks the pin before downloading; both fetchers
  add --retry-connrefused.
- mkimage rejects '.'/'..' state keys.
- ui-shot: VM liveness checked before every QMP call, console.log preserved
  as evidence on every failure path, repaint deadline widened to 90s with
  the contended-runner rationale documented.
- rs485-bridge: overflow discards back off one gap and rate-limit their log
  line, mirroring the accept-loop fix; clippy nit fixed.
- .gitignore ignores *.elf/*.map so the untracked artifacts cannot silently
  return; CI shellcheck glob now covers build/ and the rootfs boot scripts
  (directives added for the deliberate in-guest source paths).
- Docs: NPU parity row matches its sibling verification docs; line-pinned
  audit cross-references unpinned; CROSS_COMPILE documented in the build
  header; payload README lists warden-ui; ci-cd tense settled.

Verified: guards negative-tested (bad state keys, no-newline fragment);
boot smoke, portal scenario, ui-shot all PASS; 53 tests green; shellcheck
clean across the widened glob; clippy zero.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018HUayid7W5w7jBdb9Rrj1K

kernel/rv1106-enablement/npu/OPEN-NPU-PLAN.md

@@ -197,7 +197,8 @@ the whole problem.
 
 `PROVENANCE.md`: the kernel driver is portable GPL; the closed piece is the
 userspace RKNN runtime + regcmd format (a blob). **Per directive we do not ship
-that blob.** `CAPABILITIES-AUDIT.md:32` rates NPU "not worth shipping" until an
+that blob.** `CAPABILITIES-AUDIT.md`'s Remaining-blocks table rates the NPU
+"open driver VERIFIED; compute deferred" until an
 open encoder exists.
 
 ### URLs
@@ -299,5 +300,5 @@ ever begun; otherwise this is the documented reason open NPU compute is deferred
 
 ---
 _Cross-refs: `PORT-PLAN.md` (authoritative file-by-file kernel port),
-`../../docs/npu-graphics-feasibility.md`, `../CAPABILITIES-AUDIT.md:32`,
+`../../docs/npu-graphics-feasibility.md`, `../CAPABILITIES-AUDIT.md`,
 `../PROVENANCE.md`, `../DRIVER-PARITY.md:41`, `../REMAINING-PORTS.md §6`._