fix(cli): register the documented context command (#1611) (#1613)

Fixes #1611.

## What

`codegraph context <task>` has been advertised in the CLI usage header since the first commit, and the ContextBuilder behind the public `buildContext` API has always shipped in the package — but the command was never registered with commander (verified via `git log -S`: this is drift present from day one, not a removal). Invoking it errored with `unknown command 'context'`, which broke external integrations built against the documented contract — Memorix 1.8.1 invokes `codegraph context --path <project-root> --format json --max-nodes 8 --no-code <task>` and silently falls back to its own heuristic index when the command is missing.

## How

Registers `context <task...>` next to the other read commands (`query`/`explore` pattern), mapping flags 1:1 onto `BuildContextOptions`:

- `-p, --path <path>` — resolved exactly like every sibling command (nearest initialized project)
- `-f, --format <format>` — `markdown` (default) or `json`, unknown values rejected with exit 1
- `-n, --max-nodes <number>` — positive integer, validated
- `--no-code` — structure only (`includeCode: false`)

JSON output is clean, machine-parseable stdout — `error()` and warnings go to stderr — and the uninitialized-project path matches the sibling commands' error text and exit code. The usage-header line needed no change; the registered syntax matches what it has always advertised.

## Tested

New `__tests__/cli-context-command.test.ts` (modeled on `cli-query-command.test.ts`, spawning the built binary against a temp fixture): JSON parseability + shape, `--max-nodes` bounding, the exact Memorix invocation shape (`--format json --max-nodes 8 --no-code`), markdown default, uninitialized-project failure, unknown-format rejection. `npx vitest run __tests__/cli-context-command.test.ts __tests__/context.test.ts __tests__/context-ranking.test.ts __tests__/cli-query-command.test.ts` → 4 files, 39 tests, all green.

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https://claude.ai/code/session_01LxZj6W6Y1SHXwvpT3uwJpK

CHANGELOG.md

@@ -84,6 +84,8 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - Methods implemented in a generic or lifetime-parameterized `impl` block (`impl<T> Source for BufSource<T>`, `impl<'a> Iterator for Parents<'a>`) are now recorded under the implementing type instead of the trait. Previously such a method could not be found by its type — "who calls `BufSource::read`" had no answer — and it collided with the trait's own declaration, which could even invent a call-graph edge out of an impl body that contains no call at all. Impls on a reference (`impl Trait for &Foo`) and on a module-qualified type (`impl Trait for m::Foo`) are attributed to their type too. Re-index after upgrading. Thanks @Dshuishui. (#1588) (Rust)
 - A method call on a struct field — `self.inner.run()` with `inner: Inner` — now resolves to the method on the field's declared type. Previously the call was reduced to the bare method name and matched whichever same-named method was nearest, which was often the calling method itself, recording recursion that isn't in the source (a few hundred such self-edges in ripgrep alone), or a method of an unrelated type. References and `Box`/`Rc`/`Arc` fields are looked through, as Rust's own method calls are; a field whose type is external (a std or third-party type), a generic parameter, or a container like `Option`/`Vec` is left unresolved rather than guessed. Re-index after upgrading. Thanks @Dshuishui. (#1585) (Rust)
 
+- The `codegraph context <task>` command documented in the CLI help now actually exists — it builds a ready-to-inject context pack for a task (relevant symbols, their relationships, and code) in markdown or JSON, restoring the contract external integrations like Memorix rely on (`--path`, `--format json`, `--max-nodes`, `--no-code`). (#1611)
+
 ## [1.5.0] - 2026-07-21
 
 # ⚡ The Rust engine release — with near-instant sync