Remove agent-memory plugin; track UTF-8 shell config and npm manifest

agent-memory is removed: upstream (kurbezz/memory) states Windows is not supported, as the skill relies on absolute symlinks into the store and a Bash CLI. The checked-in plugins/agent-memory.js was a git symlink (mode 120000) to a Linux path, which Windows materialised as a 68-byte text file, failing to load with 'AggregateError: 7 errors building'.

Now tracked so the setup is reproducible elsewhere: opencode.json and pwsh.cmd configure the UTF-8 shell (chcp 65001) that OpenCode's -NoProfile PowerShell otherwise lacks, and package.json records better-sqlite3, without which the sqlite plugin fails to resolve.

.gitignore

@@ -19,6 +19,17 @@
 !/plugins/
 !/.gitignore
 
+# Machine config for the UTF-8 shell fix (see https://www.xsinfo.vip/windows/01-opencode-utf8.html).
+# OpenCode reads opencode.json from this directory and invokes pwsh.cmd as the shell,
+# so both are needed to reproduce a working setup on another machine. Note the shell
+# path in opencode.json is absolute and per-user, so it must be edited per machine.
+!/opencode.json
+!/pwsh.cmd
+
+# npm manifest for the sqlite plugin's better-sqlite3 dependency; without it the
+# plugin fails to load with "Cannot find package 'better-sqlite3'".
+!/package.json
+
 # Belt and braces, in case a path is ever added from the parent side.
 node_modules/
 *.log