fix(node-dev): report search matches relative to custom_nodes/ so read can open them

[wangzhengzhuo05]

What

node_pack action search reported every match path relative to the search's own path
walk root, while read / write / list_files resolve their path argument against the
custom_nodes/ base root. So a path returned by search could not be fed back into
read: it failed with NODE_DEV_ERROR: File not found under custom_nodes/: "<path>".

Reproduction from the issue: search with path set to a pack folder returns
web/js/<file>.js, and the matching read looks for custom_nodes/web/js/<file>.js.
The default path: "." happened to work only because the walk root is the base root.

How

• In searchNodePacks, compute the base root and the walk root's offset from it:

  const baseRoot = customNodesRoot(resolvedBase);
  const relPrefix = relative(baseRoot, searchDir).split(/[\\/]/).join("/");

• Pass relPrefix into both engines and prepend it to the reported file:

  • searchBuiltin: file: relPrefix ? ${relPrefix}/${rel} : rel
  • searchWithRipgrep: file: relPrefix ? ${relPrefix}/${m[1]} : m[1]

• Behavior with the default path: "." is unchanged (the prefix is empty), and the
  path/glob filtering still matches against the search-dir-relative path so glob
  semantics are untouched.

Tests

• New builtin regression test: create Pack/nodes.py, search { query: "FooNode", path: "Pack" },
  assert the reported file is Pack/nodes.py, then feed that exact string to readNodeFile
  and assert the content comes back — the full round trip from the issue.
• New ripgrep-path regression test asserting the same root-relative result through the
  mocked ripgrep seam.
• npx vitest run src/__tests__/services/node-dev.test.ts → 84 passed
• npx tsc --noEmit → clean

Mutation check

Reverting only the two file: expressions to their pre-fix form makes both new tests fail
(2 failed, 82 skipped); restoring the fix makes them pass. The new tests genuinely guard
the change.

Fixes #2921

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[wangzhengzhuo05]

Closing this to keep the tracker clean \u2014 it has been sitting without review for several days. This is no reflection on the change itself: the fix and its local verification still stand. If the issue is still present and you would like the patch revisited, say the word and I will rebase it onto current main and re-open. Thanks for your time.