fix: correct plugin install command syntax in docs (v1.4.1)

The Claude Code plugin installation is a two-step process per the official
docs at code.claude.com/docs/en/plugin-marketplaces. There is no
'claude plugin install github:owner/repo' form. Users must first add the
marketplace catalog, then install the plugin from it by name.

Fixes:

* README.md: Option 2 install section now shows the two-step flow:
    claude plugin marketplace add AgriciDaniel/claude-obsidian
    claude plugin install claude-obsidian@claude-obsidian-marketplace

* docs/install-guide.md: Same correction, same syntax.

* plugin.json: 1.4.0 to 1.4.1
* marketplace.json: 1.4.0 to 1.4.1 (both metadata.version and
  plugins[0].version)

This fixes the reported "Plugin not found in any configured marketplace"
error users see when they try the old single-command form.

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

.claude-plugin/marketplace.json

@@ -6,7 +6,7 @@
   },
   "metadata": {
     "description": "claude-obsidian: Claude + Obsidian knowledge companion by AgriciDaniel",
-    "version": "1.4.0"
+    "version": "1.4.1"
   },
   "plugins": [
     {
@@ -17,7 +17,7 @@
         "ref": "main"
       },
       "description": "Claude + Obsidian knowledge companion. Sets up a persistent, compounding wiki vault. Covers memory management, session notetaking, knowledge organization, and agent context across projects.",
-      "version": "1.4.0",
+      "version": "1.4.1",
       "author": {
         "name": "AgriciDaniel",
         "url": "https://github.com/AgriciDaniel"