Exclude gitignored files from session metadata tracking

[jcleira]

Description

When capturing file modifications in a session, skip files that are matched by the repo's .gitignore rules. Gitignored files (build artifacts, node_modules, secrets, local config) should never appear in checkpoint metadata or session transcripts, reducing noise and preventing accidental capture of sensitive local-only files.

Source

• Origin: don't track gitignored files (for example node_modules) in our session metadata as untracked_files_at_start entireio/cli#426 (changelog 0.4.6)
• Detected from: entireio-cli

Target Repos

• cli

Acceptance Criteria

• File modifications to gitignored paths are excluded from session metadata
• Gitignore rules are evaluated using the repo's .gitignore (and nested ignore files)
• Global gitignore (core.excludesFile) is also respected
• Exclusion is verified by a test that adds a file matching a gitignore pattern and confirms it is absent from the checkpoint
• No performance regression for repos with large gitignore rule sets

Context Hints

• cli/internal/session/
• cli/internal/checkpoint/
• cli/internal/git/

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Comment /minion build or add the minion-approved label to begin implementation.