Add plugin entry: bots

[prakashchokalingam]

What the plugin does

Bots adds a Bots row to the BB sidebar. Each bot has a name, an emoji
icon, its own instructions, a provider, model and reasoning level, and an
optional project. Opening a bot drops you into its newest chat, or a fresh
composer if it has none.

Bots are created as drafts and autosave every keystroke; publishing is
blocked until the bot has a name, a provider and a model, and the server
rejects startChat for a draft rather than relying on the UI to hide it.

The persona is applied through bb.agents.contributeInstructions(), which
BB evaluates at thread.start and turn.submit. The plugin maps a chat
thread back to its bot and returns that bot's instruction block, and returns
null for every other thread in BB — so a persona never leaks outside its
own chats. Both the hit and the null fallthrough are pinned by tests.

Chats are ordinary visible BB threads, so they can be opened, archived and
deleted like any other. Both chat surfaces are host-owned: the transcript is
BB's own ThreadChat and the first-message box is BB's own
experimental_NewThreadComposer. The plugin reimplements neither.

See the README screenshots for what the Bots panel looks like in BB.

Source release

• Repository: https://github.com/prakashchokalingam/bb-plugin-bots (public, MIT)
• Release: annotated tag v1.1.0, repository root, no tagPrefix
• Entry source: git.range = "^1.0.0" already covers v1.1.0, so the entry
  JSON is unchanged
• Package manifest: bb-plugin-bots@1.1.0, engines.bb >=0.39.0,
  engines.bbPluginSdk >=0.4.8

Plugin checks

• vitest run — 77 tests across 3 files, all passing
• tsc --noEmit — clean, strict: true, skipLibCheck: false
• bb plugin build — builds dist/server.js and dist/app.js + app.css
  from source; no build output is committed

Marketplace checks

• npm ci --ignore-scripts && npm run build — passes
• npm run check (liveness against the public tag) — passes
• Icon vendored at icons/bots-48f12e36.svg (1304 bytes, filename carries
  the sha256 prefix of the source SVG); no remote icon reference

Permissions and external services

The plugin makes no network calls of its own and contacts no external
service. It persists bots in a plugin-local SQLite database and holds two
in-memory maps as the read path, because contributeInstructions is a
synchronous callback on the thread-start path. Model inference happens
entirely through BB's existing provider plumbing via threads.spawn — the
plugin holds no API keys and stores no credentials.