Stack auto-detection

[JSONbored]

Problem: The loop needs to know a target repo's language, build tool, test runner, and lint/format conventions before it can safely make changes — today none of that is detected, it's assumed.

Area: AMS / Miner

Proposal: Build a detection step that inspects a target repository (manifest files, lockfiles, config files) and infers its stack and conventions before any code-generation step runs.

Deliverables:

• A stack-detection module producing a structured description (language, package manager, build command, test command, lint/format command) for an arbitrary repo.

Acceptance criteria:

• Correctly detects stack and commands for a documented set of common repo shapes.
• Fails clearly and safely (no guessing) when a repo's stack can't be confidently detected.

Test scenarios:

• Run detection against a handful of real, differently-configured repos and confirm each is described correctly.

Boundaries:

• Blocked on De-hardcode discovery from gittensory's own conventions #4784.

---

Part of #4778.

[linear-code]

JSO-3457