fix(amazonq): prevent file link click from crashing language server

[laileni-aws]

Problem

Clicking a file link in agentic chat for a file created by fsWrite crashes the language server
and loses all chat context. Two bugs combine to cause this:

1. #resolveAbsolutePath assumes any .md file not found in workspace folders is a user prompt
   file and returns ~/.aws/amazonq/prompts/<filename> without checking if it exists there.
2. onFileClicked has no error handling — when showDocument rejects because the file doesn't
   exist, the unhandled promise rejection crashes the language server process.

The fsWrite file link also never passes fullPath through the click handler data, so even when
the toolUseLookup fails to match, the fallback path resolution receives only the basename.

Solution

• Wrap onFileClicked in try/catch so a failed showDocument logs an error instead of crashing
  the server
• Add fs.exists check in #resolveAbsolutePath before returning the prompts directory path
• Fall back to description (which already contains the full absolute path) as fullPath in
  the chat-client file list mapping, reusing existing data instead of adding a redundant field

Testing

• tsc --noEmit passes for both aws-lsp-codewhisperer and chat-client packages
• Existing contextUtils tests pass
• Manual: create a .md file via fsWrite in agentic chat, click the link — should open
  correctly or log an error gracefully without crashing

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 12.50000% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.54%. Comparing base (71c53d1) to head (5632299).
⚠️ Report is 4 commits behind head on feature/file-link-not-working.

Files with missing lines	Patch %	Lines
...nguage-server/agenticChat/agenticChatController.ts	4.54%	21 Missing ⚠️

Additional details and impacted files

@@                        Coverage Diff                        @@
##           feature/file-link-not-working    #2718      +/-   ##
=================================================================
- Coverage                          60.57%   60.54%   -0.04%     
=================================================================
  Files                                279      279              
  Lines                              66275    66284       +9     
  Branches                            4253     4253              
=================================================================
- Hits                               40149    40131      -18     
- Misses                             26041    26068      +27     
  Partials                              85       85              

Flag	Coverage Δ
unittests	60.54% <12.50%> (-0.02%)	⬇️

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