Plugin version is pinned at 1.0.0, so installed caches never update

The plugin version string never changes, so Claude Code has no signal to
re-materialize an installed cache. `autoUpdate` keeps fetching the marketplace
clone, but the cache the agent actually loads keeps whatever content it had on
install day. Nothing warns the user.

`.claude-plugin/plugin.json` has said `"version": "1.0.0"` since it was added and
has never been edited since, and the `marketplace.json` entry declares no version
at all:

$ git log -p --follow -- .claude-plugin/plugin.json | grep '"version"'
+ "version": "1.0.0",

## What this looked like on my machine

Installed 2026-03-17 at `d311303`. Measured 2026-09-10:

- the loaded skills were still dated 2026-03-16
- the clone at `~/.claude/plugins/marketplaces/cloudflare` was current to `b052c32` (2026-09-07)
- 87 merged PRs and 219 commits landed in between, none of which reached the agent
- `skills/wrangler/SKILL.md` was being served at 16,937 bytes; upstream is now 6,785
- `.mcp.json` now declares one server, `https://mcp.cloudflare.com/mcp`, but my
session still had five that you have since retired: `cloudflare-api`,
`-bindings`, `-builds`, `-docs`, `-observability`

The retired server names are the part that concerns me most. Users are still
connecting to endpoints you replaced, and reading Workers guidance from March,
with no sign that anything is wrong.

## Working around it

There is no `claude plugin update` subcommand. `claude plugin marketplace update`
refreshes the clone but not the cache, and `claude plugin install` is a no-op on
an already-installed plugin. The only thing that worked was a full teardown:

claude plugin uninstall cloudflare@cloudflare
claude plugin marketplace remove cloudflare
rm -rf ~/.claude/plugins/cache/cloudflare
claude plugin marketplace add cloudflare/skills
claude plugin install cloudflare@cloudflare

Removing the marketplace also strips `autoUpdate: true` from
`extraKnownMarketplaces` in settings.json, so that needs putting back afterwards.

## Suggested fix

Bump `version` in `.claude-plugin/plugin.json` on each release, or add a
`version` to the `marketplace.json` entry, so the client has something to compare
against. The `.cursor-plugin` and `.codex-plugin` copies are pinned at 1.0.0 too,
so those clients may be affected the same way.

Start by comparing .claude-plugin/plugin.json with marketplace.json, then inspect the .cursor-plugin and .codex-plugin copies for the same pinned version. Reproduce the cache behavior with the listed Claude marketplace and install commands. Done means a released version change causes the installed cache to refresh and retired MCP server configuration is no longer served.

Written by the indexing model from the issue text.