Install Agent Skills into all 3 AI CLIs, and use Bun instead of npm

Adds scripts/install-skills.sh: pulls this repo's extensions/ skill
bundles (SKILL.md-format) at workspace startup and installs them into
Claude Code (~/.claude/skills), GitHub Copilot CLI (~/.copilot/skills),
and Antigravity CLI (~/.gemini/config/skills). Every env gets the common
awesome-skills-plugin bundle; COBOL/3D/TTRPG additionally get their
matching skill(s) from custom-specialty-plugin via a per-template
SPECIALTY_SKILLS value.

Each template also installs Bun via a coder_script and hooks ~/.bun/bin
onto PATH in .bashrc (the bun.sh installer doesn't reliably do this in a
scripted shell). The CLI setup wizard now uses `bun install -g` instead
of `npm install -g` for GitHub Copilot CLI and Claude Code CLI.

All six templates re-validated with terraform init/validate against the
real coder-server container on octo-winsrv.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/default/main.tf

@@ -267,3 +267,49 @@ resource "coder_script" "cli_setup_wizard" {
     fi
   EOT
 }
+
+# Installs Bun and uses it (instead of npm) for the CLI installs the wizard
+# script runs. The installer doesn't reliably add ~/.bun/bin to PATH in
+# non-interactive shells, so that's hooked into .bashrc explicitly here.
+resource "coder_script" "install_bun" {
+  agent_id     = coder_agent.main.id
+  display_name = "Install Bun"
+  run_on_start = true
+  script       = <<-EOT
+    #!/bin/bash
+    set -e
+    export BUN_INSTALL="$HOME/.bun"
+    if [ ! -x "$BUN_INSTALL/bin/bun" ]; then
+      curl -fsSL https://bun.sh/install | bash
+    fi
+
+    MARKER="# >>> coder bun path >>>"
+    if ! grep -qF "$MARKER" "$HOME/.bashrc" 2>/dev/null; then
+      {
+        echo ""
+        echo "$MARKER"
+        echo 'export BUN_INSTALL="$HOME/.bun"'
+        echo 'export PATH="$BUN_INSTALL/bin:$PATH"'
+        echo "# <<< coder bun path <<<"
+      } >> "$HOME/.bashrc"
+    fi
+  EOT
+}
+
+# Installs this repo's Agent Skills into Claude Code, GitHub Copilot CLI, and
+# Antigravity CLI's skills directories. See ../../scripts/install-skills.sh.
+# Default has no matching entry in extensions/custom-specialty-plugin/skills,
+# so it only gets the common awesome-skills-plugin bundle.
+resource "coder_script" "install_skills" {
+  agent_id     = coder_agent.main.id
+  display_name = "Install Agent Skills"
+  run_on_start = true
+  script       = <<-EOT
+    #!/bin/bash
+    set -e
+    mkdir -p /opt/coder
+    echo '${base64encode(file("${path.module}/../../scripts/install-skills.sh"))}' | base64 -d > /opt/coder/install-skills.sh
+    chmod +x /opt/coder/install-skills.sh
+    SPECIALTY_SKILLS="" /opt/coder/install-skills.sh
+  EOT
+}