Refactor dv-connect MCP config per-tool branches into ### subsections

## Problem

The `dv-connect` MCP configuration reference ([`references/mcp-configuration.md`](https://github.com/microsoft/Dataverse-skills/blob/main/.github/plugins/dataverse/skills/dv-connect/references/mcp-configuration.md)) marks per-tool branch boundaries with `**If TOOL_TYPE is \`x\`:**` (bold) in sections 0, 1, 2, 5, and 8.

This is the **same markdown construct** used for *within-block* step labels in those sections — e.g. `**Generate a unique server name**`, `**Update the configuration file:**`, `**Important notes:**`. So branch boundaries are not structurally distinct from the sub-steps inside a branch.

An agent parsing the file has no reliable signal for where one tool's instructions end and the next tool's begin, which risks instruction bleed across tools (e.g. applying a Cursor step during a Codex flow).

## Proposed fix

Promote each per-tool branch to a real `###` subsection so the boundary sits structurally above the `**bold**` sub-labels:

```markdown
## 5. Register the MCP server

Execute only the subsection matching your `TOOL_TYPE`; skip the others.

### 5a. Copilot
...
### 5b. Claude
...
### 5c. Cursor
...
### 5d. Codex
...
```

- Apply uniformly to every per-tool conditional section (1, 2, 5, 8).
- Add an explicit "execute only the subsection matching your `TOOL_TYPE`" routing line at the top of each.
- This is a Level-3 reference file (no token budget), so the added headings are free.

## Context

Surfaced during PR #84 review. Deferred to its own issue to keep that PR scoped to Codex enablement; this refactor touches all four tool flows and is best reviewed independently.

Start with .github/plugins/dataverse/skills/dv-connect/references/mcp-configuration.md and inspect sections 1, 2, 5, and 8, including their per-tool branches. Promote each branch to a ### subsection and add the specified routing line at the top of each conditional section. Done means all four tool flows have distinct subsection boundaries and consistent routing instructions.

Written by the indexing model from the issue text.