chore: Add Air hot-reload configuration

Adds .air.toml for air-verse/air hot-reload during development:
- Watches Go files in cmd/, internal/, pkg/
- Excludes tests, vendor, node_modules, frontend
- Automatically rebuilds on file changes
- Supports Pro build detection via HOT_DEV_USE_PRO env var
- Kill delay and graceful shutdown configured

.air.toml

@@ -0,0 +1,47 @@
+# Air configuration for Pulse hot-reload
+# https://github.com/air-verse/air
+
+root = "."
+tmp_dir = "tmp"
+
+[build]
+# Build command - uses Pro build if available
+cmd = """
+if [ -d /opt/pulse-enterprise ] && [ "${HOT_DEV_USE_PRO:-true}" = "true" ]; then
+  cd /opt/pulse-enterprise && go build -buildvcs=false -o /opt/pulse/pulse ./cmd/pulse-enterprise
+else
+  go build -o pulse ./cmd/pulse
+fi
+"""
+# Binary to run
+bin = "./pulse"
+# Watch these directories
+include_dir = ["cmd", "internal", "pkg"]
+# Exclude these patterns
+exclude_dir = ["vendor", "node_modules", "tmp", "frontend-modern", ".git"]
+exclude_file = []
+exclude_regex = ["_test\\.go$", "\\.tmp$", "~$"]
+exclude_unchanged = true
+# File extensions to watch
+include_ext = ["go", "tpl", "tmpl", "html"]
+# Kill old process before starting new one
+kill_delay = "1s"
+# Send interrupt signal first, then kill after delay
+stop_on_error = false
+# Log output
+log = "build-errors.log"
+# Colorize output
+color_main = "yellow"
+color_watcher = "cyan"
+color_build = "green"
+color_runner = "magenta"
+
+[log]
+# Show log time
+time = false
+# Only show main logs
+main_only = false
+
+[misc]
+# Delete tmp directory on exit
+clean_on_exit = true