chore(skills): drop the skill usage counters; keep the author stamp

[Leo310]

What

Removes the per-skill load and revision counters from #516, keeping the metadata.author: agent stamp that create writes.

The counters were built for a curator (on hold since the post-turn review was removed in #532), and for a person reading the Agent editor they rarely change anything. A revision already shows up as a manage_skills card in its chat and as a change to the skill note, and a bundled skill that was revised is already flagged as customized. Meanwhile every skill load wrote the plugin data file, which syncs.

Removed:

• the recording in load_skill (the recordUsage option) and in manage_skills (revisions, and forgetting on delete)
• PluginData.skillUsage, SkillUsageEntry, and the store's record/get/forget methods
• the delete-path bookkeeping in SkillsService.deleteSkill
• the usage line under custom skills in the Agent editor, and src/skills/usageSummary.ts
• the 2.3.0 changelog bullet for it

Kept: the author: agent stamp on created skills, as plain provenance in the same key the bundled skills use for S2B. Nothing in the plugin reads it; its doc comment now says so.

No migration: #516 has not shipped in a stable release. A 2.3.0 beta install keeps an unused skillUsage list in its plugin data; nothing reads it.

How I tested it

bun run check, format, lint, and the full unit suite (1989) pass. The deleteSkill test keeps its file-removal checks without the counters. Built into the S2B WT1 slot vault and reloaded with no console errors.

AI assistance: Claude Code (Fable 5.1) removed the counters from Leo's decision after discussing whether usage data is useful without a curator; Leo reviews and tests live.

Checklist

• bun run check, bun run format, bun run lint, and bun run test pass locally
• I tried the change in a real Obsidian vault (or explained above why that isn't applicable)
• I read CONTRIBUTING.md, including the section on AI assistance
• If this adds a provider, a bundled skill, a built-in tool, or changes manifest.json: I noted that the docs site needs updating (see "Documentation" in CONTRIBUTING.md) — the skills page's "Where a skill came from" is trimmed in a companion site PR

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Removes skill usage tracking from the agent editor.

The PR appears safe to merge; no actionable regression was identified.

Summary

The PR removes per-skill load and revision counters, their storage and editor display, while retaining the author stamp on agent-created skills.

• Removes counter recording from skill tools and deletion paths.
• Removes the associated data types, UI summary, tests, and changelog bullet.

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