feat: v0.7.1 — fix builtin-tools metadata, add Agent::create() alias, modularize LLM/session/tools

### Features
- Add Agent::create() alias for cross-SDK consistency (Rust/Python/Node.js)
- Add comprehensive SDK examples: sdk_basic.rs (all 11 tools) and sdk_chat.rs (LLM streaming)
- Add integration test suite (21 tests covering config, agent, tools, metadata)

### Bug Fixes
- Fix builtin-tools.md: change backend type from binary/a3s-tools to builtin
- Fix resolve_backend() fallback: return Builtin instead of Script for builtin tools

### Refactoring
- Modularize LLM client into llm/ directory (anthropic, openai, http, types, factory)
- Modularize session into session/ directory (manager, compaction)
- Extract all 11 builtin tools into tools/builtin/ directory
- Add dedicated error.rs module

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ZhiXiao-Lin

.github/setup-workspace.sh

@@ -9,10 +9,10 @@ echo "Replacing path dependencies with crates.io versions..."
 
 # core/Cargo.toml — internal crate deps
 sed -i.bak \
-  -e 's|a3s-tools-core = { version = "0.1", path = "../../tools-core" }|a3s-tools-core = "0.1"|' \
+  -e 's|a3s-common = { version = "0.1", path = "../../common" }|a3s-common = "0.1"|' \
   -e 's|a3s-lane = { version = "0.2", path = "../../lane" }|a3s-lane = "0.2"|' \
   -e 's|a3s-cron = { version = "0.1", path = "../../cron" }|a3s-cron = "0.1.2"|' \
-  -e 's|a3s-privacy = { version = "0.1", path = "../../privacy" }|a3s-privacy = "0.1"|' \
+  -e 's|a3s-search = { version = "0.6", path = "../../search", default-features = false }|a3s-search = { version = "0.6", default-features = false }|' \
   core/Cargo.toml
 rm -f core/Cargo.toml.bak