Add comprehensive build identification to agent

- Add git hash (short and full), branch, commit date
- Add build timestamp and dirty/clean state
- Add build profile (debug/release) and target triple
- New `version-info` command shows all build details
- `--version` now shows version-hash format (e.g., 0.1.0-4614df04)
- Startup logs now include version hash and build info

Example output:
  GuruConnect v0.1.0
  Git:     4614df04 (clean)
  Branch:  main
  Commit:  2025-12-30 06:30:28 -0700
  Built:   2025-12-30 15:25:20 UTC
  Profile: release
  Target:  x86_64-pc-windows-msvc

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

agent/build.rs

@@ -1,4 +1,5 @@
 use std::io::Result;
+use std::process::Command;
 
 fn main() -> Result<()> {
     // Compile protobuf definitions
@@ -7,6 +8,71 @@ fn main() -> Result<()> {
     // Rerun if proto changes
     println!("cargo:rerun-if-changed=../proto/guruconnect.proto");
 
+    // Rerun if git HEAD changes (new commits)
+    println!("cargo:rerun-if-changed=../.git/HEAD");
+    println!("cargo:rerun-if-changed=../.git/index");
+
+    // Build timestamp (UTC)
+    let build_timestamp = chrono::Utc::now().format("%Y-%m-%d %H:%M:%S UTC").to_string();
+    println!("cargo:rustc-env=BUILD_TIMESTAMP={}", build_timestamp);
+
+    // Git commit hash (short)
+    let git_hash = Command::new("git")
+        .args(["rev-parse", "--short=8", "HEAD"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .map(|s| s.trim().to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+    println!("cargo:rustc-env=GIT_HASH={}", git_hash);
+
+    // Git commit hash (full)
+    let git_hash_full = Command::new("git")
+        .args(["rev-parse", "HEAD"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .map(|s| s.trim().to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+    println!("cargo:rustc-env=GIT_HASH_FULL={}", git_hash_full);
+
+    // Git branch name
+    let git_branch = Command::new("git")
+        .args(["rev-parse", "--abbrev-ref", "HEAD"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .map(|s| s.trim().to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+    println!("cargo:rustc-env=GIT_BRANCH={}", git_branch);
+
+    // Git dirty state (uncommitted changes)
+    let git_dirty = Command::new("git")
+        .args(["status", "--porcelain"])
+        .output()
+        .ok()
+        .map(|o| !o.stdout.is_empty())
+        .unwrap_or(false);
+    println!("cargo:rustc-env=GIT_DIRTY={}", if git_dirty { "dirty" } else { "clean" });
+
+    // Git commit date
+    let git_commit_date = Command::new("git")
+        .args(["log", "-1", "--format=%ci"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .map(|s| s.trim().to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+    println!("cargo:rustc-env=GIT_COMMIT_DATE={}", git_commit_date);
+
+    // Build profile (debug/release)
+    let profile = std::env::var("PROFILE").unwrap_or_else(|_| "unknown".to_string());
+    println!("cargo:rustc-env=BUILD_PROFILE={}", profile);
+
+    // Target triple
+    let target = std::env::var("TARGET").unwrap_or_else(|_| "unknown".to_string());
+    println!("cargo:rustc-env=BUILD_TARGET={}", target);
+
     // On Windows, embed the manifest for UAC elevation
     #[cfg(target_os = "windows")]
     {