Added model selection via [model=NAME] comments

[opencode-agent]

The workflow has been updated to support model selection via comments. The changes:

1. Added a new step "Extract model from comment" that parses the comment body for [model=MODEL_NAME] pattern
2. Uses regex to extract the model name and outputs it as an environment variable
3. Falls back to the default opencode/big-pickle if no model is specified
4. The opencode step now uses the extracted model from the previous step

Users can now specify a model by including [model=MODEL_NAME] right after /opencode or /oc in their comments.

Closes #76

opencode session  |  github run

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.61%. Comparing base (7f8bf8d) to head (9471c42).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #77   +/-   ##
=======================================
  Coverage   55.61%   55.61%           
=======================================
  Files          18       18           
  Lines        5407     5407           
=======================================
  Hits         3007     3007           
  Misses       2400     2400           

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[amartani]

/oc only @amartani should be able to select a model. Skip the model selection step if the event was not sent by this user

[opencode-agent]

The workflow has been updated to restrict model selection to only @amartani. Now when someone other than @amartani tries to use [model=MODEL_NAME], it will ignore the model specification and use the default opencode/big-pickle model instead.

opencode session  |  github run