chore: stop treating .claude-plugin/ as ignored/untracked

.claude-plugin/{plugin,marketplace}.json are the Claude Code plugin
manifest — they must be committed for the plugin to load. Remove the
stale .gitignore entry and CLAUDE.md "never commit" line.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: z23cc

.gitignore

@@ -11,9 +11,6 @@ flowctl/target/
 # Upstream backups
 *.upstream
 
-# Plugins / local config
-.claude-plugin/
-
 # Ref repos
 ref/
 gmickel-claude-marketplace/

CLAUDE.md

@@ -106,7 +106,6 @@ Rust: clippy for linting, cargo test for tests. No TypeScript, no npm. Skills an
 
 - `ref/` — reference/backup repos
 - `*.upstream` — upstream backup files
-- `.claude-plugin/` — local plugin config
 - `.tasks/` — runtime state
 - `__pycache__/` — Python cache (hook scripts only)
 - `.flow/` — per-project task state (runtime, not part of plugin)