feat: add build documentation verification tool and CI workflow

[copernicusjones]

Summary

Adds automated build documentation verification to the Dasharo docs repo. This addresses bounty #1153 by creating a tool + CI workflow that verifies the documented build instructions actually produce correct binaries.

What's new

.github/scripts/verify_build.py

• Parses building-manual markdown files to extract shell build commands
• Supports device registry mapping (repo URL, coreboot target, ROM pattern)
• Runs builds inside Docker container with coreboot/coreboot-sdk:latest
• Computes SHA256 hash of built ROM for comparison against published releases
• CLI: --device/--release for single device, --all for batch, --dry-run for parsing only

.github/workflows/verify-build-docs.yml

• Triggers on PRs that modify building-manual files
• Weekly cron schedule (Monday 6am UTC) to catch documentation drift
• Manual trigger via workflow_dispatch
• Matrix strategy: tests all discovered building-manual files in parallel
• Reports parse results and command extraction status

How it works

1. Workflow finds all building-manual.md files in the repo
2. Python script parses markdown code blocks → extracts build commands
3. Commands are written to a shell script
4. (Phase 2) Docker container clones the repo at the release tag and runs the script
5. ROM hash is compared against the published SHA256 from releases.md

Next steps

• Add Docker-based actual build execution (Phase 2)
• Parse releases.md to get expected SHA256 for comparison
• Handle per-device Dockerfiles for devices with custom toolchains
• Add caching for coreboot-sdk Docker image

Closes dasharo-issues#1153