fix(file_history): colour commits by remote reachability

[dlyongemallo]

Fixes #175.

[Copilot]

Pull request overview

This PR improves file-history subject colouring by distinguishing pushed vs unpushed commits based on remote reachability (not just remote-tip decorations), and updates rendering/docs/tests to match.

Changes:

• Replace LogEntry.has_remote_ref with LogEntry.is_pushed, with a decoration-based fallback when reachability isn’t provided.
• Add Git adapter logic to precompute a “pushed commit set” via git rev-list --remotes … (including rename-aware extension for --follow / line-trace rename detection).
• Update file-history rendering to layer selection highlighting over the pushed/unpushed base highlight, and extend functional tests + docs accordingly.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
lua/diffview/vcs/log_entry.lua	Renames/repurposes the commit push-state flag and adds a fallback inference path.
lua/diffview/vcs/adapters/git/init.lua	Computes/extends a pushed commit set and passes is_pushed into LogEntry construction.
lua/diffview/scene/views/file_history/render.lua	Uses is_pushed for ref-aware subject highlighting and layers selection highlight via add_hl().
lua/diffview/tests/functional/git_adapter_spec.lua	Adds functional coverage for pushed-set computation and rename-based extension/idempotency.
lua/diffview/tests/functional/file_history_render_spec.lua	Updates subject highlight tests and validates layered selection highlight behavior.
doc/diffview.txt	Documents the new pushed/unpushed semantics and the layered selection highlight behavior.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.