feat(ui): dead code and islands — what nothing reaches, and everything that could still reach it (CG-59)

A Dead code screen and a mark on the Map, both drawn from one derivation in
src/graph/dead-code.ts so a second surface can never disagree with the first.

The SQL half is four lines — no incoming edge but `contains`. It returns ~2 500
candidates on this repository and the shipped list is 20; everything in between
is the feature. A candidate is dropped the moment there is any reason to believe
something outside the graph reaches it: exported symbols and header
declarations, test and generated files, abstract and interface members, anything
carrying a `decorates` edge, overrides of an ancestor's member, names the
language calls by itself, vendored directories, files nothing in the index
reaches (those are islands, and the Map says so instead), names the resolver
failed to resolve somewhere, and names shared with a symbol that IS referenced —
the mis-resolution that leaves a used method with a self-edge and its twin with
nothing. The last rule is the only one that is not a graph query: before a claim
is made, the declaring file and every file that reaches it are read and the
identifier counted, which is what catches the references the extractor never
recorded (`this.handleMessage.bind(this)`, a call inside an object literal, a
shorthand property).

Every subtraction is counted and printed under the list with the scale it came
from, and the caveat line above it never collapses: the claim is "no static
reference in the index", not "unused".

On the Map a module nothing depends on keeps its stroke and says so in its count
line, and tool-generated files and modules recede to ink-4 there, in the map's
file list, in search results and on the file screen.

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

CHANGELOG.md

@@ -72,6 +72,14 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
   Members that redeclare something from a type above are marked in the outline ("overrides Base", or "satisfies Clock" for an interface), so a 40-member class shows at a glance which parts are its own and which are a contract it is filling. The number of implementations shown here is the same number `codegraph_explore` reports to your agent when it announces an interface dispatch.
 
+- **Find the code nothing reaches, in `codegraph ui`.** A new **Dead code** tab lists the symbols no import, call or reference anywhere in your project reaches — biggest first, grouped by the file they live in, with the number of lines each one would take with it. A class nobody uses brings its methods along as a single finding rather than eleven. Every row opens the code.
+
+  The screen is built to be believed rather than to look impressive. A line above the list says, and keeps saying, that this means "no static reference in the index" and not "unused" — reflection, a framework registry and a template can all reach code a graph cannot follow. Under the list, every reason a candidate was left off is printed with its count, so you can see the list is twenty findings out of two and a half thousand candidates rather than twenty out of twenty-one.
+
+  Those exclusions are the feature. Anything exported, or declared in a header, is off the list by default, because something outside your repository can import it — one switch adds them back, with a warning band. So are test and generated files, abstract and interface declarations, anything a decorator registers, members that override something further up, names the language calls for you (`constructor`, `__enter__`, `main`), vendored directories, and files nothing in your project reaches at all. Two more rules catch what the graph itself missed: a name CodeGraph failed to resolve somewhere is never called unreferenced, and neither is a name shared with a symbol that *is* used — the twin may simply have been picked instead. Last, before any row is shown, the files that could reach it are read and the identifier counted: written down twice, something uses it and we did not see it.
+
+  On the **Map**, a module nothing depends on now says so in its own count line instead of counting itself — usually your entry points, sometimes something you forgot to delete. Tool-generated files and modules are dimmed wherever they appear: on the map, in its file list, in search results and on the file screen.
+
 ### Fixes
 
 - Fixed a long-running `codegraph ui` session serving a symbol that a sync had already deleted. The viewer keeps one connection to your index open, and its in-memory lookup didn't notice when another process — your agent's sync, or `codegraph sync` — rewrote the file underneath it, so a symbol screen could keep showing a body with no callers while search correctly reported it had moved. Because a symbol's identity includes the line it starts on, this happened after almost any edit above it.