feat(ui): the Flow strip — how one symbol reaches another, one card per hop (CG-50)

Ask "how does execute reach getFile" in the search box and the viewer draws the
call path between them, left to right, opening every card at the exact line that
makes the next call. Dynamic-dispatch hops are dashed and name the site they
were wired at; "Read as flow" turns a trail walked by hand into the same strip.

The path finder is NOT new. `codegraph_explore` already leads its answers with
the longest call chain among the symbols an agent named, and a viewer that drew
a different path would get the two quoted against each other in a review. So the
search moved out of `ToolHandler` into `src/graph/named-symbol-flow.ts` and both
callers ride it — same tokens, same overload rules, same synthesized edges. What
stayed behind in `tools.ts` is the prose.

A pinned from/to question is the same search with two options changed, because
both ends being named is the evidence explore's one-unnamed-bridge cap stands in
for: it bridges freely, keeps twelve candidates per endpoint instead of six
(the CLI's own `main` sorts seventh of ten), and searches from both ends at once
— identical paths to the one-way walk on twelve measured pairs, 3-6x faster.

`/api/flow` is deliberately the one endpoint with no cache: its cards carry
source read from disk, and a drift verdict changes without the index changing.

Verified on this repo (`execute` to `rowToFileRecord`, 8 hops; `main` to
`resolveOne`, 7) and on a fresh excalidraw index, where `mutateElement` to
`renderStaticScene` crosses callback, react-render and jsx-child hops and lists
exactly the hops `codegraph_explore` prints.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -26,6 +26,12 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
   It opens on your project's source directory; a picker switches to any other top-level folder or the whole repository, a checkbox brings tests in, and `depth` splits a large folder into its sub-folders — useful on a monorepo. What you're looking at lives in the address, so the view is shareable.
 
+- **Ask how one symbol reaches another, in `codegraph ui`.** Type "how does execute reach getFile" into the search box — or `execute -> getFile` — and the Flow strip draws the call path between them, left to right, one card per hop. Each card is opened at the exact line that makes the next call rather than at the top of the function, so reading the strip is reading the handful of lines that actually carry the work; the identifier being called is a link, and clicking a card opens it in the symbol screen with the trail already set to the path you've read so far.
+
+  A dashed link is a hop nobody can see in the source — a callback, an interface dispatch, a React re-render, a JSX child — and it names the mechanism and, where CodeGraph knows it, the exact line the handler was wired at. When a name means several definitions, the strip says so and names the one the path runs through, offers the alternatives in a picker, and can draw them together as one branching diagram. "Not connected" is an answer rather than a failure: a flow that runs through a dispatch no static edge records genuinely has no path, and the screen says so instead of inventing one.
+
+  The **"Read as flow"** button on the trail turns a walk you did by hand into the same strip. It is the same path finder `codegraph_explore` leads its answers with, so the picture and what your agent tells you can't disagree.
+
 
 ## [1.6.0] - 2026-08-26