Support optional editor context in GitHub issue investigation

[tninja]

This pull request enables the "Investigate issue" command (C-c a v with the mode selection of "Investigate issue") to optionally include local editor context such as the current active file name, current function (via which-function), active region text, list of other visible files in the window, and pinned repository context.

Changes

• Updated ai-code-pull-or-review-diff-file and its downstream helper ai-code--pull-or-review-pr-with-source in ai-code-github.el to accept a prefix argument arg.
• Introduced an interactive check using y-or-n-p to prompt the user if they want to include the editor context when investigating a GitHub issue (if any editor context is available).
• Updated ai-code--build-issue-investigation-init-prompt to build the Local Context block and append it to the investigation prompt if requested.
• Fixed mock functions inside test/test_ai-code-github.el to properly handle variadic/optional arguments, and added a TDD-oriented unit test checking correct prompt generation and context embedding.

Verification

• Ran checkdoc and byte-compilation on modified Emacs Lisp files ensuring no warnings or errors.
• Verified that all 33 tests in test_ai-code-github.el pass successfully.

Closing #395

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Honor pinned context outside file buffers

When Investigate issue is invoked from a non-file buffer such as Magit status, pinned repository context can still be available because ai-code--format-repo-context-info keys off default-directory, but this guard returns the base prompt before checking it (and the caller mirrors the same buffer-file-name/region test). As a result C-u/include-context silently drops the stored repo context, which is one of the advertised context sources; build the blocks first or include repo/visible context in the availability test.

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[chatgpt-codex-connector]

Load discussion helpers before using regions

When ai-code-github is loaded without ai-code-discussion and the user has an active region and accepts context, this call is reached but the helper is only declared, not required, so Emacs signals (void-function ai-code--get-region-location-info) before sending the prompt. The explain-code-change branch requires ai-code-discussion, but the issue-investigation context path needs the same require or an fboundp guard before using the region helper.

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