[FEATURE]: Show active session skills in the UI (sidebar, like MCP/TODO/LSP) and keep the model aware of them during the session

Describe the enhancement you want to request

Problem

Today, opencode's interface already surfaces important session state on screen: connected MCP servers, the agent's TODO list, LSP status. But skills — arguably one of the most important harness components — are invisible once a session starts. The only way to see them is the one-shot /skills picker (#7846), and after that there's no persistent indication of which skills are attached to the session.

This causes two real problems:

1. For the user: I can't tell at a glance which skills are active in the current session. If a skill isn't firing, I have no idea whether it's even loaded.
2. For the model: In long sessions, the model loses track of available skills. Skills get mentioned in the system context early on, but as the conversation grows, the model "forgets" they exist and doesn't invoke the skill tool even when the task clearly matches a skill's trigger description. It ends up reinventing workflows the skill already encodes.

Proposed solution

UI side (visible in TUI/web/desktop):

• Add an "Active skills" panel to the right sidebar / status area, alongside the existing MCP, TODO and LSP indicators, listing the skills attached to the current session (name + source, e.g. project .opencode/skills/ vs global ~/.config/opencode/skills/ vs plugin-provided).
• Make each entry indicate its state: available vs invoked this session.
• Clicking/selecting an entry could show its description and trigger conditions.

Harness side (the more valuable half of this request):

• Actively re-assert loaded skills during the session so the model doesn't drift away from them. Options to consider:
  • inject a compact "active skills" reminder into the context periodically or on compaction (skills are especially likely to be dropped during context compaction);
  • or include a short skills availability line in tool-result/system context so late-session turns still see "you have these skills available and should use the skill tool when a task matches".

This would be a genuine harness improvement, not just cosmetics: skills only help if the model actually remembers to use them.

Related (checked before filing)

• #7846 — /skills command to list and quick-invoke skills (one-shot dialog; this request is about persistent visibility + model awareness).
• #48252 — Desktop "Environment panel" (read-only inventory of skills/plugins/MCPs for Desktop; this request focuses on the in-session sidebar indicator like MCP/TODO/LSP and on the model not forgetting skills).
• #7533 / #6154 — TUI skills in status/sidebar.

Happy to test early builds — I run a skill-heavy setup and hit the "model forgot the skill" problem regularly.