Backend: Add Anthropic/Claude provider integration

- Add anthropic.rs module with streaming support
- Convert between internal and Anthropic tool/message formats
- Add keyring dependency for secure API key storage
- Add API key management commands (get_exists, set)
- Auto-detect provider from model name (claude-* prefix)
- Support SSE streaming from Anthropic API
- Handle tool calling with Anthropic's format
- Add cancellation support for Anthropic streams

src-tauri/Cargo.lock

@@ -960,6 +960,17 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "eventsource-stream"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "74fef4569247a5f429d9156b9d0a2599914385dd189c539334c625d8099d90ab"
+dependencies = [
+ "futures-core",
+ "nom",
+ "pin-project-lite",
+]
+
 [[package]]
 name = "fastrand"
 version = "2.3.0"
@@ -1988,6 +1999,16 @@ dependencies = [
  "unicode-segmentation",
 ]
 
+[[package]]
+name = "keyring"
+version = "3.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eebcc3aff044e5944a8fbaf69eb277d11986064cba30c468730e8b9909fb551c"
+dependencies = [
+ "log",
+ "zeroize",
+]
+
 [[package]]
 name = "kuchikiki"
 version = "0.8.8-speedreader"
@@ -2074,8 +2095,10 @@ version = "0.1.0"
 dependencies = [
  "async-trait",
  "chrono",
+ "eventsource-stream",
  "futures",
  "ignore",
+ "keyring",
  "reqwest",
  "serde",
  "serde_json",
@@ -2162,6 +2185,12 @@ version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
 
+[[package]]
+name = "minimal-lexical"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
+
 [[package]]
 name = "miniz_oxide"
 version = "0.8.9"
@@ -2276,6 +2305,16 @@ version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
 
+[[package]]
+name = "nom"
+version = "7.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d273983c5a657a70a3e8f2a01329822f3b8c8172b73826411a55751e404a0a4a"
+dependencies = [
+ "memchr",
+ "minimal-lexical",
+]
+
 [[package]]
 name = "num-conv"
 version = "0.1.0"