fix: correct context pruning order and vector alignment

- Prune context BEFORE processing (LSTM forget gate pattern)
  so LLM only sees relevant context, instead of pruning after the fact
- Fix ensureTrained() to recompute all event vectors after retraining
  vectorizer, fixing feature-space mismatch between stored vectors and
  query vector that made relevance scoring effectively random
- Add read lock to knowledge BuildTree() (data race fix)
- Log writeIndex() errors instead of discarding them
- Fix TOCTOU race in document ContextToDoc() dedup
- Fix healthcheck timing (measure elapsed before cleanup)
- Refactor waiter CLI into separate files (state, conn, config, editor,
  history, builtin) for maintainability
- Add CLI plugin API key authentication

cmd/waiter/builtin.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func handleBuiltin(cmd string, cfg *Config, state *State, reconnect func()) bool {
+	switch {
+	case cmd == "/help":
+		fmt.Println(`Built-in commands:
+  /help                    show this help
+  /exit, /quit             exit waiter
+  /clear                   clear screen
+  /reconnect               force reconnection
+  /connect <path>          switch to a different unix socket
+  /remote <url>            switch to remote HTTP mode
+  /local                   switch back to local socket mode
+
+Server commands (sent to agent):
+  /status                  system status
+  /kernel                  kernel status
+  /settings [prefix]       list settings
+  /settings set <k> <v>    set a setting
+  /plugin list             list installed plugins
+  /plugin install <url>    install plugin
+  /plugin remove <name>    remove plugin
+  /plugin info <name>      plugin details
+  /memory query <text>     query graph memory
+  /knowledge               list knowledge base
+  /agents                  list agents
+  /chat <text>             send to agent
+
+Any other text is sent to the agent directly.`)
+		return true
+
+	case cmd == "/exit" || cmd == "/quit":
+		return true
+
+	case cmd == "/clear":
+		fmt.Print("\033[H\033[2J")
+		return true
+
+	case cmd == "/reconnect":
+		printlnC(colorYellow, "reconnecting...")
+		reconnect()
+		return true
+
+	case strings.HasPrefix(cmd, "/connect "):
+		cfg.Socket = strings.TrimSpace(cmd[9:])
+		cfg.Remote = ""
+		reconnect()
+		return true
+
+	case strings.HasPrefix(cmd, "/remote "):
+		cfg.Remote = strings.TrimSpace(cmd[8:])
+		cfg.Socket = ""
+		reconnect()
+		return true
+
+	case cmd == "/local":
+		cfg.Remote = ""
+		cfg.Socket = discoverSocket("")
+		reconnect()
+		return true
+
+	default:
+		return false
+	}
+}