Migrate the web runner, mcpdo and TUI bundles from tsup to tsdown #2797

Follow-up to #1492, which recommended migrating and moved clients/cli to tsdown as the prototype.

Remaining builds

In the order recommended by docs/tsdown-migration.md:

1. Web runner: clients/web/tsup.runner.config.ts. A single entry with no JSX: the CLI change applied to a different file.
2. mcpdo: clients/mcpdo/tsup.config.ts. Two entries (mcp-bin, mcpdod), so shared chunks. Check how src/daemon/ensure.ts resolves mcpdod.js against Rolldown's chunk naming.
3. TUI: clients/tui/tsup.config.ts. JSX goes to inputOptions.transform.jsx, and ink-form / ink-scroll-view go to deps.alwaysBundle. __tests__/tsupConfig.test.ts imports tsup's Options type and needs rewriting against tsdown's config type, keeping its React-externals assertions.

Per client

• deps.neverBundle built from a const EXTERNALS = [...] expanded with subpath patterns. A bare string matches the exact specifier only, so subpaths are otherwise inlined silently.
• fixedExtension: false and outputOptions.comments: { jsdoc: false }, as in clients/cli/tsdown.config.ts.
• Drop tsup. Drop the esbuild override / allowScripts entries only once npm ls esbuild is empty in that install; web probably keeps them for Vite.
• Update BUNDLED_CLIENTS in scripts/verify-bundle-externals.mjs, the external-list paths in AGENTS.md and scripts/sdk-watch.mjs, and the config name in the client's tsconfig include.

Acceptance

• No tsup dependency remains in any client.
• verify:bundle-externals, each client's test:coverage and local:gate pass.
• Each bundle emits the same set of bare imports as before.