fix: security hardening and code quality

- SQL query mode uses read-only SQLite connection with PRAGMA query_only=ON
- Lua sandbox removes dofile/loadfile/load after OpenBase to block file access
- Plugin manager sorts by priority once at load time; GetPlugins is a plain copy
- Proxy appends [body truncated] marker when body hits size limit
- App startup exits with os.Exit(1) on DB open failure
- tickCmd uses tea.Tick instead of time.Sleep in a goroutine
- ErrMsg with non-nil error shows notification then quits
- DB stores path for use by read-only query connection
- WAL journal mode + NORMAL synchronous set in migrate()
- config.go uses errors.Is(err, os.ErrNotExist)
- main.go uses os.UserHomeDir() and removes racy port pre-check
- findings renderer is cached and rebuilt only on width change

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

internal/config/config.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	_ "embed"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -67,7 +68,7 @@ func Load(path string) error {
 	viper.SetConfigType("yaml")
 	viper.SetConfigFile(path)
 	if err := viper.ReadInConfig(); err != nil {
-		if !os.IsNotExist(err) {
+		if !errors.Is(err, os.ErrNotExist) {
 			return err
 		}
 	}