fix: moving header sections when inserting snippets

[gavinbarron]

When a markdown file's tab section terminator '---' is the very last line with no trailing blank line, two issues occurred:

1. Accessing originalFileContents[currentIndex + 1] without bounds checking caused an IndexOutOfRangeException crash.
2. The '---' line was not included in the removable splice range, leaving a stray terminator in the output.

Fix by setting snippetsTabSectionEndLine to currentIndex + 1 as an exclusive end so the '---' line is always included in the splice range. Remove the trailing blank line peek which was only needed as a workaround for the old inclusive index and which, when combined with the +1 fix, would over-remove and displace subsequent headers like '### Response' into the tab section.

Clamp the FileSplicer offset when insertionLine falls past the end of the array after the splice (EOF edge case).

[Copilot]

Pull request overview

Fixes edge cases in markdown snippet-tab replacement when the tab terminator (---) appears at EOF (no trailing blank line), preventing crashes and ensuring the terminator is properly removed without displacing subsequent headers.

Changes:

• Adjust tab-section end handling to treat the --- line as part of the removable splice range (exclusive end index) and remove a bounds-unsafe “peek” for a trailing blank line.
• Add/adjust unit tests for EOF terminator behavior and for ensuring following headers (e.g., ### Response) are not moved into the tab section.
• Update the “comment on first line” test to assert current behavior (no injection) instead of only asserting “no throw”.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
ApiDoctor.Console/Program.cs	Updates tab-section end detection to avoid out-of-range access and ensure --- is included in the splice range.
ApiDoctor.Console.UnitTests/ProcessSnippetInjectionTests.cs	Refines and expands tests around EOF terminators and header displacement scenarios.

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