fix(hermes): preserve YAML list indentation (2-space flush style)

[marcosdanielsf]

Summary

The Hermes installer target assumed list items were indented 4 spaces under their parent key, but YAML accepts both the 4-space style and the more common 2-space flush style:

```yaml

flush (2 spaces) — broke before this fix

platform_toolsets:
cli:

• hermes-cli
• mcp-codegraph

nested (4 spaces) — worked before, still works

platform_toolsets:
cli:
- hermes-cli
- mcp-codegraph
```

Two bugs surfaced on flush-style configs:

1. `childRange()` used `/^ \S/` to detect sibling keys, so a list item like ` - mcp-codegraph` was misread as the next child key — the range closed early and `upsertCodeGraphToolset` either failed to find the `cli` block or inserted into the wrong place.
2. When appending a new entry, the installer hardcoded 4-space indentation, mixing styles inside a single list.

Fix

• Tighten the sibling-key regex in `childRange()` to require an actual mapping key (`^ [A-Za-z_][\w-]*:`), so list lines no longer terminate the range.
• Add `listItemIndent()` to detect the indentation of existing list items and reuse it when appending `- mcp-codegraph`.
• Default the bootstrap insert (when no `cli:` block exists yet) to 2-space flush style, matching the in-repo Hermes config format.

Test plan

• Existing test suite updated to assert the flush-style output (` - hermes-cli` instead of ` - hermes-cli`).
• `npm test -- tests/installer-targets.test.ts` — 82/82 passing locally.
• Reproduced the original break against a real Hermes config with flush-style lists; with this patch the installer is idempotent on both styles.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Detect sibling keys that have inline YAML values

The new sibling-boundary regex only matches lines like " key:" and ignores valid siblings such as " other: { ... }" or " discord: [ ... ]". In those configs, childRange() no longer stops at the next sibling, so calls like removeCodeGraphMcpServer()/upsertCodeGraphMcpServer() and upsertCodeGraphToolset() can treat subsequent sibling entries as part of the current block, leading to accidental deletion or malformed insertion when rewriting the file.

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[chatgpt-codex-connector]

Handle quoted and numeric sibling YAML keys

The new boundary check in childRange() assumes sibling keys must match [A-Za-z_][A-Za-z0-9_-]*, but YAML allows keys like 'x.y': and 1st:. In files that use those valid key forms under mcp_servers or platform_toolsets, range detection runs past the actual sibling boundary, so install/uninstall can splice through unrelated sections instead of only the target child block.

Useful? React with 👍 / 👎.