[Feature Request] Interactive per-session plugin selection at task start

Bug Description
Feature request: per-session plugin picker at task start

Add interactive plugin selection when starting a new session/task, similar to agtx (https://github.com/fynnfluegge/agtx#plugins). Currently enabledPlugins in settings.json is static and /plugin enable|disable requires manual mid-session invocation.

Desired behavior:

• On session start, optionally prompt user to select which installed plugins to activate for this session
• Selection scoped to the current session, not global settings
• Configurable: opt-in via setting (e.g., promptPluginsOnStart: true) so users who want static config aren't disrupted
• Ideally exposed as a SessionStart hook capability that can drive the native prompt UI (AskUserQuestion-style), so custom pickers can be built

Use case: different tasks need different plugin sets (security review vs. frontend work vs. data analysis). Toggling globally pollutes context with irrelevant slash commands/skills/MCP tools across all sessions. Per-session scoping keeps each task's tool surface minimal and intentional.

Workaround today: maintaining multiple project dirs with different enabledPlugins, or manually running /plugin disable repeatedly. Both are friction-heavy.

Environment Info

• Platform: darwin
• Terminal: ghostty (cmux)
• Version: 2.1.131
• Feedback ID: 384c7f50-866d-4d9a-bd50-62814270a275

Errors

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