Add single-job GH Actions workflow for all package builds

[Copilot]

The existing unified-build.yml fans out each of the 44 packages into separate jobs, requiring per-job system dep installs and artifact upload/download between every dependency pair. This adds significant overhead and complexity.

Changes

• New workflow .github/workflows/single-job-build.yml — single build-all job with all 44 packages as sequential steps
• Shared filesystem eliminates artifact passing; make install in each step makes outputs immediately available to subsequent steps
• One-time dep install — all system packages installed once at job start instead of redundantly per job
• Tier-ordered steps — T0→T1→T2→T3→T4→T5 preserves dependency ordering; atomspace-storage, unify, and spacetime are built first within T2 since later tiers depend on them
• Per-step continue-on-error: true — mirrors the existing continue-on-error behavior per package; a single build failure does not abort the rest
• Consolidated log artifact — all build logs collected into one build-logs artifact instead of per-package uploads

Structure comparison

	unified-build.yml	single-job-build.yml
Jobs	~45	1
Artifact passes	~44 upload + ~100 download	0
System dep installs	Per job	Once
Steps	~300	47

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