feat: add 15 offline Git phrases and verify work preservation

[nawaaaaaAaar]

Summary

Closes #8. Add 15 beginner Git phrases to the offline seed dictionary, using the existing placeholder conventions and without requiring an AI provider.

Includes status, unstaged/staged diffs, branch inspection/creation/switching, commit history, staging/saving work, stashing, and undoing the last commit with reset --soft so working content is preserved.

Verification

• Complete Python suite: 460 passed on Python 3.12, including the dictionary-format gates.
• New regression resolves actual seed suggestions and executes them in an isolated synthetic Git repository, verifying branches, staging, commit messages and soft-reset preservation of file content/index.
• bash tests/test_shell_functions.sh: 69 passed, two failed. Identical upstream failures concern classifying go build and go mod tidy; Go is absent here. Not represented as a full shell-suite pass.
• ShellCheck warning-level check of clishe.sh and install.sh: passed.
• git diff --check: passed.

No remote repository, credentials, provider APIs or real user worktree was used. Runtime safety and placeholder handling are unchanged.

Prepared with Perplexity Computer assistance; no personal account-owner review is claimed.

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