feat(installer): stop auto-indexing on install + ship opt-in front-load prompt hook

`codegraph install` no longer indexes the current directory — it wires up agents
only, and building a project's graph is always the explicit `codegraph init` /
`index`. Removes the global-vs-local inconsistency (a local install silently
indexed, a global one didn't) and the docs/behavior mismatch (#826). README
updated to match; the stale `init --index` note (indexing is default now) fixed.

Adds an opt-in Claude Code front-load hook: a `UserPromptSubmit` hook that runs
the new hidden `codegraph prompt-hook`, which injects codegraph_explore context
for structural ("how / where / trace / impact") prompts so the agent answers
from the graph instead of grepping to rebuild it. Prompted at install
(default-yes; Claude-only — the only agent with prompt hooks), removed on
uninstall, and `codegraph upgrade` self-heals it onto an already-configured
global Claude install. Strictly additive + degradable: non-structural prompts,
un-indexed projects, and any failure are silent no-ops. Disable without
uninstalling via CODEGRAPH_NO_PROMPT_HOOK=1.

7 new installer-targets contract tests (write / idempotent / opt-out round-trip /
sibling-preserved / uninstall / legacy-independent). Full suite green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -11,6 +11,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### New Features
 
+- **Claude Code:** an optional front-load hook makes your agent reach for CodeGraph automatically. When you ask a structural question — "how does X work", "what calls Y", "trace the flow from A to B" — CodeGraph injects the relevant source and call paths into the prompt up front, so the agent answers from the graph instead of grepping around to rebuild it. You're asked during `codegraph install` (default yes; Claude Code only, since it's the agent with prompt hooks), it's removed by `codegraph uninstall`, and `codegraph upgrade` turns it on for existing Claude setups. It's strictly additive and degradable — non-structural prompts and un-indexed projects are left alone — and you can switch it off any time without uninstalling by setting `CODEGRAPH_NO_PROMPT_HOOK=1`.
 - Vue store actions, mutations, and getters are now indexed as symbols you can find and read. Whether your store is **Vuex** (`mutations` / `actions` objects in a module) or **Pinia** — both the options form (`defineStore({ actions: { … } })`) and the setup form (`defineStore('id', () => { … })`, where actions are local functions) — each action, mutation, and getter is now a real node. So `codegraph search` finds `login` or `getSessionList`, and `codegraph_explore` / `codegraph_node` show its body and what it calls, instead of "not found" because the function only existed as an object-literal property.
 - `codegraph_explore` now connects a Vue component to the **Pinia** store action it calls. When code does `const store = useUserStore()` and then `store.fetchUser()`, that call now links through to the `fetchUser` action in the store module — so "what happens when this view loads its data?" traces from the component into the action's body instead of stopping at the `store.fetchUser()` line. Works for both Pinia store styles (options and setup), and stays precise (a built-in like `store.$patch()` or an unrelated same-named method isn't mislinked).
 - `codegraph_explore` now follows **Vuex** string dispatch. A `dispatch('user/login')` or `commit('SET_TOKEN')` call — namespaced `'module/action'` keys included — now links to the action or mutation it names, resolved to the correct store module even when several modules share an action name (and without being fooled by a same-named `api/` helper). So "what runs when this dispatches?" traces from the call into the store handler and on to the mutations it commits. Vuex's canonical `export default { namespaced, actions, mutations }` module shape is now indexed too, so those handlers are findable symbols.
@@ -30,6 +31,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixes
 
+- `codegraph install` now wires up your agents and stops there — it no longer indexes the current directory. Building a project's graph is always the explicit `codegraph init` (or `codegraph index`), so you decide what gets indexed and when, and the steps are the same whether you installed globally or just for one project. This clears up the confusion where a project-local install silently indexed but a global one didn't, and where the docs and the tool disagreed about whether you still had to run `init`. (#826)
 - React components declared with `forwardRef`, `memo`, or styled-components / emotion (`const Button = forwardRef(...)`, `const Card = memo(...)`, `const Box = styled.button\`…\``) are now recognized as components, so finding where they're used works. Before, they were indexed as plain constants, so `codegraph callers` and impact analysis reported "no callers found" even when the component was rendered across dozens of files — a dangerous false "safe to change" right before refactoring a shared component. Now every `<Button/>` usage links back to the component, so callers and blast radius are complete. This is the standard shadcn/ui declaration style, so for typical React design systems the whole UI layer is no longer invisible to impact analysis. Thanks @Arlandaren for the report and @maxmilian for the root-cause. (#841)
 - React Router and Next.js routes defined in `.tsx` / `.jsx` files are now indexed. Routes written as JSX — `<Route path="/users" element={<UsersPage/>}/>`, `createBrowserRouter([...])`, and Next.js `app/`/`pages/` page files — were being skipped entirely (only routes that happened to live in plain `.ts`/`.js` were picked up), so "what renders at this path?" and the route → page-component link were missing for most React apps. Now those routes show up in `codegraph search`/`codegraph_explore` and connect to the component they render, just like the backend route → handler links on other frameworks.
 - `codegraph sync` (and the file-watcher auto-sync behind always-on / MCP use) no longer drops a function's callers when you edit the file that function lives in. Re-indexing a file after an edit — even a docstring-only change — was severing the `calls` / `references` edges coming from *other, unchanged* files (e.g. `from pkg import mod; mod.fn()` callers, or any cross-file reference), so `codegraph callers` / `impact` would abruptly report "no callers" for a function that's used throughout the codebase, until the next full re-index. Sync now preserves those incoming cross-file edges across the re-index, re-matching them to the symbol even when the edit shifted its line number. Most visible in large Python package trees, but it applies to every language. Thanks @JosefAschauer. (#899)