Index the H2 2026 roadmap in the README guide list and the AGENTS.md docs/ tree #2002

Found by Copilot reviewing the v2.2.0 milestone merge (#1993). This is the deferred half of #1980 / #1981, which nothing was tracking.

#1981 added docs/inspector-roadmap-2026-h2.md and said so explicitly:

Index updates deferred. The docs-maintenance rule would normally have this PR also add the file to the root README.md guide list and the AGENTS.md docs/ tree. Both are deliberately left out to keep this diff to the document itself, and will follow separately.

"Separately" never got an issue, so the deferral had no way to come back. Meanwhile the file is now merged and shipping to main in the v2.2.0 release, undiscoverable from either index:

• README.md:52-57 — the "Task-oriented guides live under docs/" list names four guides; the roadmap is absent.
• AGENTS.md — the docs/ entry in the project tree reads (v1-to-v2-migration.md, mcp-server-configuration.md, mcp-app-review.md, launcher-config-consolidation-plan.md, images/), so the documented tree is stale.

Both are what the "Keep documentation files up to date" rule requires when a file is added.

Scope

1. Add a bullet to the README guide list with a one-line description (the two-track structure — spec-following vs. chosen UX work — and the 🟢/🟡/🔴 tagging).
2. Add inspector-roadmap-2026-h2.md to the docs/ line of the AGENTS.md project tree.

Nothing else — this is deliberately just the indexes the originating PR left out.