feat: support webhook payload passthrough and dynamic notification recipients

[huanghongbo-hhb]

Background

Workflow needs to pass through code-related context from webhook triggers and support dynamic recipients in IM notifications based on payload / author fields.

Changes

• Pass through TARGET_BRANCH, COMMITTER, COMMIT_ID, COMMIT_MESSAGE, and PR for webhook-triggered workflows
• Flatten webhook payload into runtime variables so it can be referenced directly in notification templates
• Support using payload fields as notification recipient values via dynamic_recipients
• Fix runtime context overwrite in retry / manual execution scenarios that caused build output data loss
• Reuse the legacy Feishu webhook sending path and align URL encoding / proxy handling

Verification

• GitHub PR webhook triggers workflow successfully
• TARGET_BRANCH / COMMITTER / COMMIT_ID are passed through correctly
• {{.payload.pull_request.user.login}} and other payload fields can be resolved
• Mail / Feishu dynamic recipients can be sent successfully
• Build image name and output variables are preserved in retry / manual execution scenarios

Note

• GitLab was not fully validated in this chain.

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