feat: add AWS Bedrock AgentCore browser provider (native Rust) (#397)

* feat: add AWS Bedrock AgentCore browser provider (native Rust)

- Add agentcore provider with SigV4 authentication
- AWS SDK deps are optional behind 'agentcore' feature flag
- Build with: cargo build --features agentcore
- Supports AGENTCORE_REGION, AGENTCORE_PROFILE_ID, AGENTCORE_BROWSER_ID env vars
- Returns session ID and Live View URL in launch response
- Add connect_cdp_with_headers for signed WebSocket connections

* test: add unit tests for AgentCore provider

* refactor: use lightweight manual SigV4 signing instead of AWS SDK

- Replace aws-sigv4/aws-config with manual HMAC-SHA256 signing
- Removes ~60s compile time and significant binary size
- Credentials read from AWS_ACCESS_KEY_ID/AWS_SECRET_ACCESS_KEY env vars
- Supports AWS_SESSION_TOKEN for temporary credentials

* fix: correct AgentCore API endpoints

- Host: bedrock-agentcore.{region}.amazonaws.com
- Start session: PUT /browsers/{id}/sessions/start
- Stop session: PUT /browsers/{id}/sessions/stop
- Add urlencoding for browser ID in path
- Add AWS_DEFAULT_REGION fallback

* fix: use profileConfiguration.profileIdentifier for AgentCore profile

The AWS Bedrock AgentCore API expects profile configuration in the format:
{
  "profileConfiguration": {
    "profileIdentifier": "<profile-id>"
  }
}

Not the flat "profileId" field that was previously used.

* feat: support AWS credential provider chain via AWS CLI

- Try env vars first (AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY)
- Fall back to 'aws configure export-credentials --format env'
- Honor AWS_PROFILE environment variable
- Works with SSO, IAM roles, credential files, etc.

---------

Co-authored-by: Chris Tate <chris@ctate.dev>

cli/Cargo.toml

@@ -10,6 +10,10 @@ readme = "../README.md"
 keywords = ["browser", "automation", "ai", "cdp", "chrome"]
 categories = ["command-line-utilities", "web-programming"]
 
+[features]
+default = []
+agentcore = ["hmac", "hex", "chrono", "urlencoding"]
+
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
@@ -31,6 +35,12 @@ similar = "2"
 zip = { version = "8.2.0", default-features = false, features = ["deflate"] }
 time = { version = "0.3", features = ["formatting"] }
 
+# AgentCore provider (optional - lightweight SigV4 signing)
+hmac = { version = "0.12", optional = true }
+hex = { version = "0.4", optional = true }
+chrono = { version = "0.4", optional = true }
+urlencoding = { version = "2", optional = true }
+
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"