ci: Extract manifest specs from workflow to config.yml

[Copilot]

During recent CI additions, explanatory comments were removed from build scripts, and manifest configuration remained embedded in the workflow file instead of being extracted to config like the path detection logic.

Changes

Restored comments in docker/linux/build.sh

• Added section comments matching debian_build.sh style (Ubuntu config, multi-arch setup, variant logic, default target)

Restructured .github/config.yml schema

# Before: flat structure
debian:
  paths: [...]
ubuntu:
  paths: [...]

# After: distro-centric organization
debian:
  ci:
    paths: [...]
  manifests: [10 manifest configs]
ubuntu:
  ci:
    paths: [...]
  manifests: [5 manifest configs]

Each distro is now a top-level key with nested ci.paths (for path-based detection) and manifests (for OCI specs) sections, making the configuration more intuitive and self-contained.

Updated .github/workflows/build.yml

• Extract manifests from config using jq: .debian.manifests | map(. + {tag: (.tag | gsub("{sha}"; "..."))}) | {manifests: .}
• Reduced workflow from 288 to 196 lines
• Path detection now reads from .debian.ci and .ubuntu.ci
• Manifest generation reads from .debian.manifests and .ubuntu.manifests

Manifest configs use {sha} placeholder for runtime substitution instead of inline template expansion.

Original prompt

if you look at the last commit you will see some ci addition

in the course of dev i told you to remove your comments but then you just removed all - i actually wanted the comments that were there already

relatedly you will see that we added a yaml config file and then parsed it - i want to do the same for the other yaml that is currently just embedded in the wf - and to do that we need to rethink the schema for .github/config.yml to accomodate both use cases

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[phlax]

@copilot i think make the schema more like

ubuntu:
  ci:
    paths:
    ...
  manifests:
  ...
debian: etc

[Copilot]

@copilot i think make the schema more like

...

Restructured the schema as requested. Each distro is now a top-level key with ci.paths and manifests sections. Workflow filters updated to match the new structure. See commit cefa443.