feat: include file path and line number in PR review comments

[xmtp-coder-agent]

Resolves #81

Summary

• Extracts path and line from pull_request_review_comment webhook payloads
• Adds a File: <path>:<line> line to the formatted message sent to Coder tasks
• Only appears for inline review comments (not general PR comments or review submissions)

Changes

• src/webhook-router.ts — Extract filePath and lineNumber from review comment payloads
• src/webhook-router.ts — Add optional fields to PRCommentContext type
• src/handler-dispatcher.ts — Pass new fields through to handler
• src/handlers/pr-comment.ts — Add fields to interface and forward to message formatter
• src/messages.ts — Include File: line in output when file path is present

Example output

New Comment on PR: https://github.com/org/repo/pull/1#comment-1
Commenter: reviewer
Timestamp: 2026-03-17T12:00:00Z
File: src/handlers/pr-comment.ts:42

[INSTRUCTIONS]
...

Test plan

• New test: formatPRCommentMessage includes file path and line number
• New test: formatPRCommentMessage includes file path without line number
• New test: formatPRCommentMessage omits file line when not provided
• New test: PR comment handler includes file/line in forwarded review comment
• New test: Webhook router extracts filePath and lineNumber from review comment fixture
• All 187 tests pass, typecheck/lint/format clean

Note

Include file path and line number in PR review comment messages

• Extends PRCommentContext and CommentMessageParams with optional filePath and lineNumber fields, populated from the webhook payload's comment.path and comment.line.
• formatPRCommentMessage now appends a File: <path>[:<line>] line to the formatted message when filePath is present.
• The WebhookRouter extracts these fields from pull_request_review_comment events and passes them through to the handler via the dispatch context.

^{Macroscope summarized a4a1bce.}