feat(code): tree-sitter symbol extraction + auto-indexing

Symbol extraction (symbols.rs):
- tree-sitter parsers for Rust, TypeScript, Python
- Extracts: functions, structs, enums, traits, classes, interfaces
- Signatures, docstrings, line ranges for each symbol
- extract_project_symbols() walks project directory
- Skips hidden/vendor/target/node_modules, files >100KB

Proto: IndexSymbols + SymbolEntry messages for client→server symbol relay

Client: after SessionReady, extracts symbols and sends IndexSymbols
to Sol for indexing into the code search index.

14 unit tests for symbol extraction across Rust/TS/Python.

Cargo.lock

@@ -4017,6 +4017,12 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
 
+[[package]]
+name = "streaming-iterator"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b2231b7c3057d5e4ad0156fb3dc807d900806020c5ffa3ee6ff2c8c76fb8520"
+
 [[package]]
 name = "strsim"
 version = "0.11.1"
@@ -4074,6 +4080,10 @@ dependencies = [
  "tonic",
  "tracing",
  "tracing-subscriber",
+ "tree-sitter",
+ "tree-sitter-python",
+ "tree-sitter-rust",
+ "tree-sitter-typescript",
  "tui-markdown",
 ]
 
@@ -4654,6 +4664,55 @@ dependencies = [
  "tracing-log",
 ]
 
+[[package]]
+name = "tree-sitter"
+version = "0.24.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5387dffa7ffc7d2dae12b50c6f7aab8ff79d6210147c6613561fc3d474c6f75"
+dependencies = [
+ "cc",
+ "regex",
+ "regex-syntax",
+ "streaming-iterator",
+ "tree-sitter-language",
+]
+
+[[package]]
+name = "tree-sitter-language"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "009994f150cc0cd50ff54917d5bc8bffe8cad10ca10d81c34da2ec421ae61782"
+
+[[package]]
+name = "tree-sitter-python"
+version = "0.23.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d065aaa27f3aaceaf60c1f0e0ac09e1cb9eb8ed28e7bcdaa52129cffc7f4b04"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
+[[package]]
+name = "tree-sitter-rust"
+version = "0.23.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca8ccb3e3a3495c8a943f6c3fd24c3804c471fd7f4f16087623c7fa4c0068e8a"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
+[[package]]
+name = "tree-sitter-typescript"
+version = "0.23.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c5f76ed8d947a75cc446d5fccd8b602ebf0cde64ccf2ffa434d873d7a575eff"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
 [[package]]
 name = "try-lock"
 version = "0.2.5"