ci: reduce hosted-runner queue amplification

[blakinio]

Objective

Reduce avoidable GitHub-hosted runner occupancy and queue amplification without weakening required CI.

Implemented

• general CI classifies compile, fast, and lua scope before allocating reusable jobs;
• documentation/task-only changes skip unrelated Fast Checks, Lua Syntax, and Windows builds;
• CI / Required fails closed on scope/result mismatches and still requires Windows success for non-draft compile changes;
• intentional cancelled CI conclusions are no longer automatically retried; timeout and proven startup-failure retry remain;
• Windows build fanout is reduced from 5 hosted jobs to 3: CMake Release, CMake Tests, and one Solution job that builds Debug/OpenGL/DirectX after one VS/v145 + vcpkg setup;
• existing Solution artifact names are preserved.

Live validation

Exact head b082c62fdd13896e27321a86e2bccf2d46c41abc:

• Track A agent runtime governance: success;
• Detect Build Scope: success;
• Lua Syntax: success;
• Fast Checks static analysis: success;
• yamllint/actionlint/XML validation: success;
• emitted Windows graph is exactly 3 hosted jobs, not 5: CMake Release, CMake Tests, Solution Debug + OpenGL + DirectX;
• combined Solution job completed one VS 2026/v145 + vcpkg setup and is executing all three configurations sequentially;
• all three Windows jobs must finish successfully before merge.

Safety

• no build configuration or required compile gate is removed;
• compile scope still implies both fast-check and Lua prerequisites;
• merge queue/manual validation force full scope;
• no self-hosted runner is made required while Synology availability remains unproven;
• post-merge docs-only closeout must prove only scope detector + aggregate Required allocate general-CI runners;
• no owner-funded AI/Codex/OpenAI quota is used.

Task: OTC-20260816-actions-concurrency-optimization.

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[blakinio]

Superseded by the owner-authorized Linux-only hybrid CI change. The repository's ordinary CI/build/test lane will use GitHub-hosted Linux runners; Windows build gates are being removed. Dedicated Synology/self-hosted capacity remains reserved for real runtime/LAN/display/persistent-environment work and is intentionally kept separate. The useful queue-reduction ideas from this PR will be carried forward where they remain applicable, without preserving the Windows gate.

[blakinio]

Superseded by #331. Converting this obsolete PR to draft solely to emit its existing converted_to_draft CI event in the same concurrency group, which cancels the orphaned Windows run without starting another Windows build. The PR will then be closed again.