⬆️ feat: upgrade tunnel-doctor to v1.2.0 with Layer 4 SSH ProxyCommand diagnostics

Add fourth conflict layer: SSH ProxyCommand double tunneling causing
intermittent git push/pull failures when Shadowrocket TUN is active.

Structural improvements per skill best practices:
- Eliminate content duplication between SKILL.md and reference
- Rename proxy_fixes.md → proxy_conflict_reference.md for clarity
- Trim SKILL.md from 534 to 487 lines (under 500 limit)
- Shorten YAML description from 910 to 661 characters
- Fix "apply all four" listing 5 items (separate anti-pattern)
- Clarify Layer 4's relationship to Tailscale theme

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

.claude-plugin/marketplace.json

@@ -732,10 +732,10 @@
     },
     {
       "name": "tunnel-doctor",
-      "description": "Diagnoses and fixes conflicts between Tailscale and proxy/VPN tools (Shadowrocket, Clash, Surge) on macOS. Covers three conflict layers: route hijacking, HTTP proxy env var interception, and system proxy bypass. Includes SOP for remote development via SSH tunnels with proxy-safe Makefile patterns. Use when Tailscale ping works but SSH/HTTP times out, when browser returns 503 but curl works, when setting up Tailscale SSH to WSL instances, or when bootstrapping remote dev environments over Tailscale",
+      "description": "Diagnoses and fixes conflicts between Tailscale and proxy/VPN tools (Shadowrocket, Clash, Surge) on macOS. Covers four conflict layers: route hijacking, HTTP proxy env var interception, system proxy bypass, and SSH ProxyCommand double tunneling. Includes SOP for remote development via SSH tunnels with proxy-safe Makefile patterns. Use when Tailscale ping works but SSH/HTTP times out, when browser returns 503 but curl works, when git push fails with failed to begin relaying via HTTP, when setting up Tailscale SSH to WSL instances, or when bootstrapping remote dev environments over Tailscale",
       "source": "./",
       "strict": false,
-      "version": "1.1.0",
+      "version": "1.2.0",
       "category": "developer-tools",
       "keywords": [
         "tailscale",
@@ -749,6 +749,8 @@
         "ssh-tunnel",
         "autossh",
         "proxy",
+        "proxycommand",
+        "git-push",
         "networking",
         "macos",
         "makefile",