feat: add Trim Large Session command (v0.8.5)

Fixes 400 "unexpected end of JSON input" errors caused by oversized sessions
(60MB+) exceeding API provider payload limits. The trim operation:
- Keeps init/system lines + last N message turns (default 400)
- Backs up original to .jsonl.bak-TIMESTAMP before overwriting in-place
- Session ID unchanged so existing CC entry point still works
- Available via Repair menu > Trim, and as inline button on session tree items

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

Author: Myoontyee

package.json

@@ -2,7 +2,7 @@
   "name": "claude-code-exporter",
   "displayName": "Claude Code Exporter — Claude Code, Codex & Cursor Conversation History",
   "description": "Export AI coding agent conversations to Markdown. Supports Claude Code (→ .claude-code-history/), OpenAI Codex (→ .codex-history/), and Cursor Composer (→ .cursor-history/). Features: auto-watch, session inject/import for claude --resume, and repair of thinking-block signature errors when switching API providers.",
-  "version": "0.7.7",
+  "version": "0.8.5",
   "publisher": "myoontyee",
   "engines": {
     "vscode": "^1.85.0"
@@ -114,6 +114,12 @@
         "icon": "$(wrench)",
         "category": "Claude Code Exporter"
       },
+      {
+        "command": "claudeCodeExporter.trimSession",
+        "title": "Trim Large Session (Keep Recent Messages, Backup Original)",
+        "icon": "$(fold)",
+        "category": "Claude Code Exporter"
+      },
       {
         "command": "claudeCodeExporter.renameWorkspace",
         "title": "Rename This Workspace Folder (Keep AI Conversations Linked)",
@@ -179,6 +185,11 @@
           "command": "claudeCodeExporter.injectSession",
           "when": "viewItem == session",
           "group": "inline@3"
+        },
+        {
+          "command": "claudeCodeExporter.trimSession",
+          "when": "viewItem == session",
+          "group": "inline@4"
         }
       ]
     },