Release CLI v0.1.81 with Gateway semantic projection

[AntoineToussaint]

Publish the production Gateway semantic-index transport merged in #270.

DOD:

• immutable v0.1.81 tag targets the exact merged-main release commit;
• downloadable CLI release is published by the tag workflow;
• source-workspace registry selects the released semantic-capable agents;
• Mind consumes v0.1.81 and Core v0.2.80 without local replacements;
• real JVM/.NET semantic projection passes through the released generic agent.