feat: make context optional

[jhult]

Summary

Makes the context store feature optional via Cargo feature flags. Context—grite's distributed file/symbol index that AI agents can query to understand project structure—is still enabled by default, but can now be disabled at compile time to reduce binary size and compilation time by excluding tree-sitter and language grammar dependencies.

Changes

Features

• Added context feature flag to grite, libgrite-cli, libgrite-core, and libgrite-git crates
• Made all tree-sitter dependencies optional (12 crates: tree-sitter, streaming-iterator, and 10 language grammars)
• Context remains enabled by default for backwards compatibility

Refactoring

• Added #[cfg(feature = "context")] guards to context-related CLI commands, types, store methods, event handlers, and tests
• Updated libgrite-ipc to use default-features = false for libgrite-core

Files Changed

Type	Files
Modified	19

Key files:

• crates/libgrite-core/Cargo.toml - Feature flag definition with optional tree-sitter deps
• crates/libgrite-core/src/store/mod.rs - Conditional context store fields and methods
• crates/grite/src/cli.rs - Conditional context subcommand
• crates/libgrite-cli/src/types.rs - Conditional context option/result types

Test Plan

• cargo test - Context tests run with default features enabled
• cargo test --no-default-features - Tests compile and pass without context feature
• cargo check --no-default-features - All crates compile successfully without context
• cargo build - Binary builds with context enabled by default
• cargo build --no-default-features - Binary builds successfully without context