fix(plugins): move hand-written skills from .agents/skills/ to skills/ (#164)

* fix(mastra): move use-mastra skill to skills/ per repo convention

The hand-written use-mastra skill was added at .agents/skills/use-mastra/
in #161, but .agents/skills/ is reserved for vendor-managed skills.sh
output tracked in skills-lock.json (see CLAUDE.md). Move it to the default
skills/ location and switch the plugin.json skills field to array form
["./skills/", "./.agents/skills/"] so both paths load. No skill content
changed.

Refs #161

* fix(better-auth): move use-better-auth skill to skills/ per repo convention

The hand-written use-better-auth skill was added at .agents/skills/use-better-auth/
in #159, but .agents/skills/ is reserved for vendor-managed skills.sh
output tracked in skills-lock.json (see CLAUDE.md). Move it to the default
skills/ location and switch the plugin.json skills field to array form
["./skills/", "./.agents/skills/"] so both paths load. No skill content
changed.

Refs #159

* chore: revert manual CHANGELOG and version bumps (release-please owns them)

Both CHANGELOG.md and plugin.json version are auto-managed by
release-please for plugins/* (see release-please-config.json
extra-files: [{ jsonpath: "$.version" }] and existing release
PRs #158/#160/#163). Manual edits race with the next release PR.

Skill relocations and the plugin.json `skills` array change remain
intact — they're the actual fix release-please will pick up via the
fix(...) commits already on this branch.

Author: amondnet

plugins/better-auth/.claude-plugin/plugin.json

@@ -14,5 +14,5 @@
     "auth",
     "typescript"
   ],
-  "skills": "./.agents/skills/"
+  "skills": ["./skills/", "./.agents/skills/"]
 }

…/.agents/skills/use-better-auth/SKILL.md …ter-auth/skills/use-better-auth/SKILL.mdplugins/better-auth/.agents/skills/use-better-auth/SKILL.md renamed to plugins/better-auth/skills/use-better-auth/SKILL.md plugins/better-auth/.agents/skills/use-better-auth/SKILL.md renamed to plugins/better-auth/skills/use-better-auth/SKILL.md

@@ -24,5 +24,5 @@
       ]
     }
   },
-  "skills": "./.agents/skills/"
+  "skills": ["./skills/", "./.agents/skills/"]
 }