ui(memory): capitalize --table headers and shorten UUID column

[codeaholicguy]

Fixes #240

Summary:

• Capitalize memory search table headers and show 8-character ID prefixes in table output.
• Keep JSON search output unchanged with full IDs.
• Add a dim empty-state tip and update the --table help text.

Validation:

• npm ci
• cd packages/agent-manager && npm run build
• cd packages/channel-connector && npm run build
• cd packages/memory && npm run build
• cd packages/cli && npx vitest run
• cd packages/cli && npx tsc --noEmit
• cd packages/cli && npx oxlint src
• npx prettier --write packages/cli/src/commands/memory.ts packages/cli/src/tests/commands/memory.test.ts
• npm run lint
• npm run test

Risks: none known.