agent-instructions doc doesn't cover worktree instances or e2e/webServer port reuse

[nonreagent]

Problem

An agent working in a git worktree of a consumer project needed to run e2e tests. The test runner's webServer config reuses an already-running local server rather than starting a fresh one. The agent had to reason through, from scratch, that:

• the worktree's own dev server isn't running, but the main checkout's adj-supervised instance is, on a fixed port
• if it let the e2e runner "reuse" that port, it would test the main checkout's code under the worktree's test run
• the fix was to boot an unsupervised dev server on an alternate port and point the e2e run at that

That workaround reintroduces exactly what Adjacent exists to prevent — an unlogged, unsupervised process outside the daemon's lifecycle — instead of registering a worktree instance (adj add --label) and pointing the e2e run at <label>.<name>.adj.ac.

Root cause

adj agent-instructions (crates/adj/src/agent_docs.rs) is the only steering doc consumer-project agents see, and it says nothing about:

• worktrees at all — no mention that adj add inside a linked worktree gets its own routed hostname, process, port, and logs
• e2e/test-runner integration — no guidance on pointing a webServer/reuseExistingServer-style config at the adj-proxied hostname instead of a bespoke local port

The README's "Worktrees" section (lines 79–85) and "Agent Integration" section exist independently; nothing connects them for an agent deciding how to run tests against a worktree instance.

Proposal

Extend the agent-instructions template (and/or the README) with a short section covering:

• worktree instances get their own hostname/port/process — don't spin up a second unsupervised server for one
• for test runners that reuse an existing local server by port (Playwright's webServer.reuseExistingServer is the common case), point baseURL/webServer.url at the instance's <name>.adj.ac (or <label>.<name>.adj.ac in a worktree) instead of hardcoding a port

Acceptance criteria

• adj agent-instructions output mentions worktree instances and how to address them
• Output gives concrete guidance for e2e/test-runner configs that reuse an existing server by port
• agent_docs.rs unit test asserts the new section renders