TypeScript/JavaScript literal receivers bind a confident false edge — `"x".replace()` hits an unrelated user function (#59)

## What is wrong

In every TypeScript and JavaScript codebase ripwire indexes, a built-in method call can link to an
unrelated user function that happens to share its name. `"a-b".replace(…)`, `[3, 1, 2].map(…)` and
`/x/.test(s)` all do it. The graph's ambiguity gauge stays at zero, so the wrong edge reads as
confident, and an agent is sent to code that never runs. This is issue #59.

An earlier fix vetoed built-in method names wholesale and was backed out, because it deleted true
edges: on webpack, `--callers=stringify` went from 361 to 0. The safe first step is to decide by the
receiver's **type**, not its name — starting with receivers whose type the syntax already proves,
which is to say literals. Everything else keeps today's behaviour.

## The evidence

`test/fieldnarrowcheck.sh` carries a KNOWN GAP block on a freshly generated fixture, rewritten
minimally from #59's own reproduction:

- Five arms pin today's wrong behaviour — a string, a template, an array, a regex, and a chain
starting from a string literal. Each binds an unrelated function in `src/unrelated.ts`, with
`graph_ambiguous="0"`. They pass today. **Flipping them is the finish line.**
- Two controls pin true edges any fix must keep: a typed user-object receiver `r.replace()` binding
`Rewriter.replace`, and `"x".shout()` binding the repo's own `String.prototype.shout`.
- A presence guard keeps the block from passing vacuously.

Confirm the arms pass today with `bash test/fieldnarrowcheck.sh` on a plain dev build.

## Size

**Medium.** The code is small: a receiver classification at extraction (an append-only enum, with a
version bump and its mirror) and one resolver arm. Most of the work is measurement — establishing
the *full* population of edges the change removes on a real corpus, not a sample. webpack is the
historical corpus for this one.

## Where to start

`prompts/help-wanted/ts-literal-receivers.md` is a self-contained prompt for a coding agent. It
carries why this matters, the file pointers, the rejected attempt and why it failed, the
reproductions, the design space and constraints, the acceptance criteria, the known traps — every
one of them measured on `main` while the kit was written — and what the fix PR's description should
contain. Like every prompt in `prompts/`, **it ends by writing a plan and stopping** — a maintainer
agrees the plan before any code is written.

Nothing else has to merge first; the gap is on `main` today.

Comment here to claim it.

Read prompts/help-wanted/ts-literal-receivers.md first, then run bash test/fieldnarrowcheck.sh on a plain dev build to confirm the current behavior. Measure the full edge population on webpack, preserving the typed-object and String.prototype.shout controls; done means the five literal-receiver arms no longer bind unrelated functions without deleting true edges.

Written by the indexing model from the issue text.