Add enterprise config-dir sync (config-as-code) and ConfigFile tracking

[duaraghav8]

Motivation

• Provide configuration-as-code for MCPJungle by loading desired-state entity configs from a directory (default ~/.mcpjungle).
• Ensure config-managed entities are reflected in the DB and in-memory state and kept in sync live when files change.
• Track which entities are managed via files (vs created by CLI/API) so only those are reconciled by the sync manager.
• Enable this behavior only in enterprise mode to limit scope to enterprise deployments.

Description

• Introduces a ConfigFile model to track config-managed files and adds auto-migration for it (internal/model/config_file.go, internal/migrations/migration.go).
• Adds a configsync.Manager that loads JSON files from ~/.mcpjungle subdirectories (mcp_servers, mcp_clients, tool_groups, users), applies desired state via existing services, watches for changes with fsnotify, debounces events, and prunes removed files (internal/service/configsync/manager.go).
• Adds config-driven upsert helpers for MCP clients and users so file configs can create/update entities (internal/service/mcpclient/mcp_client.go, internal/service/user/user.go).
• Wires startup to enable the config sync manager in enterprise mode and cleanly stop it on shutdown, and adds github.com/fsnotify/fsnotify to go.mod (cmd/start.go, go.mod).

Testing

• No automated tests were executed for this change.

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Codex Task

[duaraghav8]

addresses #142