go-live 9/9: write the v1 to v2 migration guide

[cliffhall]

Phase 9 of 9 in the v2 go-live runbook — see #1804 (§10). Pairs with #1803.

Write the v1 → v2 migration guide.

This is the highest-value doc shipped alongside the swap. CLI flags changed substantially, and --config semantics are genuinely different in v2 (read-only session file, with --catalog as the writable one). Without this, the deprecation notice sends people somewhere confusing.

Tasks

• CLI flag mapping, v1 → v2.
• --config vs --catalog semantics, with before/after examples.
• Node engine requirement change (>=22.7.5 → >=22.19.0).
• What no longer ships: the inspector-client / inspector-server / inspector-cli sub-packages (v2 is a single tarball).
• Link it from the deprecation notice, the 2.0.0 release notes, and the docs site (docs: new modelcontextprotocol.io Inspector documentation for v2 (legacy vs. modern era, more screenshots) #1803).

[cliffhall]

Triage: Priority = High

Scored 9/16 with the priority rubric added to AGENTS.md in #1891. This card is already approved and sitting in Todo — only Priority was set here, its Status is unchanged.

Axis	Score	Reasoning
Severity / impact	3/5	A docs gap rather than a defect, but a consequential one: CLI flags changed substantially and --config semantics genuinely differ in v2, so the deprecation notice currently sends people somewhere confusing with no map.
Urgency / staleness	4/5	The trigger already fired — v2 is published and v1 is deprecated — so the guide is late relative to the event it was meant to accompany, and the #1872 sweep has just pointed 135 reporters at v2.
Signal bonuses	+2	milestone (v2.2.0) (+1), assigned (+1)
Total	9	Lands in the High band (9-11).

Related issues. These look connected and may be worth reading together:

• Execute the first v2/main → main milestone merge and cut the release #1876 — the release this guide was scoped to ship alongside
• docs: new modelcontextprotocol.io Inspector documentation for v2 (legacy vs. modern era, more screenshots) #1803 — the paired documentation work for modelcontextprotocol.io
• Triage the open issue backlog: backfill v1/v2 labels, close legacy, board the rest #1872 — the deprecation sweep that just directed a large group of v1 users toward v2

Scores are a starting point, not a verdict — the rubric is meant to be overruled when it's plainly wrong, provided the reason is written down.