Add web widget hide buttons

[edwin-zvs]

Summary

• add a per-widget [-] hide button to the web UI widget title row
• show the widget selector dropdown in the web UI so hidden widgets can be re-expanded
• keep the widget popover open while checking or unchecking widgets from the selector
• wire both controls through the same persisted visible-widget state
• keep long widget titles truncated so the hide control remains reachable
• extend web smoke coverage for hide button rendering, selector visibility, selector toggle behavior, persistence, and menu unchecked state

Validation

• node script parse check for the inline web UI script
• cargo build
• cargo test -p agentd-e2e web_client_loads_and_websocket_connects -- --nocapture
• git diff --check

Built debug binaries

• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agent
• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agentd
• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agentd-mcp
• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agentd-adapter-antigravity
• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agentd-adapter-claude
• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agentd-adapter-codex
• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agentd-adapter-shell
• /Users/moon/agentd/.claude/worktrees/webui-widget-hide-buttons/target/debug/agentd-adapter-zarvis

Relevant binary: this PR changes daemon web UI assets, so run agentd to test the web client behavior.