Update Engine and CLI release references

[konojunya]

Background

Engine 0.9.1 contains the corrected arrow terminal geometry, and CLI 0.5.4 is now published from the matching Engine dependency. Documentation generation still uses Engine 0.9.0 and advertises CLI 0.5.3.

Implementation Approach

• Pin @stack-sh/engine 0.9.1 for generated render fixtures and live WASM resources.
• Pin CLI 0.5.4 to its exact release commit.
• Regenerate all locale pages, the agent workflow, the skill, and the integrity manifest.

Testing Approach

• npm run release:sync
• npm run release:check
• npm run generate
• npm run check
• npm run machine:check
• npm test
• STACK_CLI_BIN=/absolute/path/to/stack-0.5.4 npm run smoke
• git diff --check

Review Perspectives / Points of Concern

• Generated content changes are limited to the pinned Engine package, CLI release identity, rendered version declarations, and their integrity hashes.
• The smoke test exercised the generated skill and all four localized first-render walkthroughs with the 0.5.4 binary.