docs: the codegraph ui section, changelog entry and telemetry posture (CG-47)

A new user can now reach the viewer from the README alone: a "Read your
graph in the browser" section with a screenshot re-shot from the real
build, a step 5 in Get Started, a CLI Reference row, and the same
content as a docs-site guide.

- README: new section (what the three columns are, the options, the
  privacy posture), Contents entry, Get Started step 5, CLI row.
  Screenshot at assets/codegraph-ui-symbol-view.png, version-tagged ?v=1.
- CHANGELOG: an [Unreleased] New Features entry in the user-facing voice.
- codegraph help ui: mentions the `web` alias, says what the screen shows,
  and states that nothing is sent anywhere.
- TELEMETRY.md: the viewer has no telemetry of its own and makes no
  outbound connections; the only thing recorded is the command name in
  the daily rollup, which every off-switch already suppresses.
- site/: guides/viewer.md + sidebar entry, a `ui` section in the CLI
  reference, and a link from Next Steps.

src/bin/codegraph.ts

@@ -20,7 +20,7 @@
  *   codegraph callees <symbol>   Find what a function/method calls
  *   codegraph impact <symbol>    Analyze what code is affected by changing a symbol
  *   codegraph affected [files]   Find test files affected by changes
- *   codegraph ui [path]          Open the browser viewer for an indexed project
+ *   codegraph ui [path]          Open the browser viewer for an indexed project (alias: web)
  *   codegraph upgrade [version]  Update CodeGraph to the latest release
  */
 
@@ -1878,10 +1878,16 @@ Examples:
   $ codegraph ui ~/code/my-app      Read a specific indexed project
   $ codegraph ui --port 8080        Use one specific port (fails if it's taken)
   $ codegraph ui --no-open          Just print the URL (headless boxes, SSH)
+  $ codegraph web                   Same command under its alias
+
+Pick a symbol and you see who calls it on the left, its source in the middle,
+and what it calls on the right at the height of the line that calls it. Search
+with / (or Cmd-K), click a file path for the file's outline and its imports.
 
 The viewer listens on 127.0.0.1 only, so nothing on your network can reach it,
 and it is read-only: it opens an index that already exists and never changes
-your project or your graph. Requests from any other host are refused.
+your project or your graph. Requests from any other host are refused, and
+nothing is sent anywhere: no code, no paths, no analytics.
 
 Without --port it takes ${DEFAULT_UI_PORT}, or the next free port if that one is busy.