feat(packaging): define versioned Artisan Street layout

[sandersonstabo]

Dependency

• Immediate parent: Backend Conversation Subscription Registrar #330 (agent/backend-conversation-subscription-registrar-port-1bf42a5)

Scope

• Add the closed v2 Artisan Street versioned installation-layout contract.
• Freeze logical executable roles ae, installer, editor, and forge, with .exe only on Windows.
• Validate strict version/path safety, exact stable/versioned member sets, case-fold collisions, missing/undeclared members, forbidden Broker, and disabled production fallbacks.
• Register the focused Rust proof in package and root Bazel gates.

Exclusions

• No binary target convergence, archive migration, payload staging, signing, installer behavior, runtime launch, or legacy two-binary archive changes.

Verification

• Exact-head packaging gate3 passed: focused build; 9 Rust tests; fresh direct Clippy; root rustfmt; locked/offline Cargo metadata; LF-only contract; exact five-path hashes/status; Bazel shutdown 0.
• Receipt: D:/artisan-editor-gate-logs/portable-versioned-layout-v2-20260829-gate3/receipt.json.

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Summary by cubic

Adds the frozen v2 Artisan Street versioned installation-layout contract and a source-only Rust proof that enforces it before later packaging work. No binary, archive, installer, or runtime behavior changes.

Details

• Freezes executable roles ae, installer, editor, and forge, with .exe only on Windows.
• Validates exact stable and versioned member sets for Windows and non-Windows targets.
• Rejects unsafe version or path components, case-fold collisions, missing or undeclared members, the Broker role, and enabled production fallbacks.
• Registers the proof in root and packaging Bazel gates.

^{Written for commit 19975ca. Summary will update on new commits.}