Show loaded skills in TUI sidebar context panel

[maiconfaria]

Problem

When an agent loads a skill, there is no visual feedback in the TUI. Users cannot tell which skills are currently in context without running opencode debug skill.

Proposed solution

Display loaded skills alongside the existing sidebar entries (session name, context usage, LSP status). Collapsed state shows a count, expandable to list names. Mirrors the existing LSP pattern.

Prior art

• PR feat: show skills in status and sidebar #6154 had a working implementation with a GIF
• Issue [FEATURE]: display loaded skills in status page and sidebar #7533 requested this but was closed as not planned

Why revisit

Skills are a growing feature. Without sidebar visibility, the user's mental model of agent context is incomplete.

[Necmttn]

Loaded skills are part of the active context contract, so the sidebar should show more than a count. Useful fields: skill name, source path or package, loaded vs invoked, load trigger, token/byte estimate, and last refresh time. That makes skill context inspectable without forcing users into a debug command after the model has already acted on those instructions.

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