feat: remove old installer, update docs to npx claude-mem

Removes installer/ directory (16 files) — fully replaced by src/npx-cli/.
Updates install.sh and installer.js to redirect to npx claude-mem.
Adds npx claude-mem as primary install method in docs and README.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.npmignore

@@ -5,7 +5,6 @@ tests/
 docs/
 datasets/
 private/
-installer/
 antipattern-czar/
 
 # Heavy binaries installed at runtime via smart-install.js