feat(init): 👻 bootstrap Git Intent with fix-author

[yonathan9669]

Summary

Bootstraps Git Intent around its first concrete workflow.

Introduces the project contract, community contribution surface, and
git-fix-author as the first deterministic, recovery-aware reference
operation.

Why

Simple Git intentions frequently require fragile low-level procedures.

Git Intent moves that procedural complexity into reviewed operations that can
be invoked equally by humans and agents:

Express the Git intent, not the surgery.

Included

• public project positioning, philosophy, architecture, and operation contract;
• MIT license, contribution guidance, security policy, and code of conduct;
• Agent Skills-compatible git-fix-author package;
• one canonical executable for human and agent use;
• dry-run, interactive, and deterministic non-interactive modes;
• explicit author/committer semantics without Git configuration mutation;
• native recovery refs before reachable refs move;
• atomic updates for affected local branch tips;
• post-rewrite verification of trees, messages, timestamps, topology, and
  identities;
• disposable-repository integration tests;
• skill validation and Linux/macOS CI; and
• issue forms centered on operation intent and safety contracts.

Lessons incorporated

The reference operation accounts for failure modes identified during both the
original exploration and this implementation:

• previews never invoke a pager;
• the engine does not depend on an interactive rebase or editor;
• the executing user's configured identity cannot leak into rewritten commits;
• author, committer, and co-author semantics remain distinct;
• root commits, empty commits, and merge topology are supported;
• commit messages are copied from raw commit objects rather than pretty output;
• related local refs move in one transaction and are disclosed in the preview;
• the current branch and working tree need not change when another branch is
  targeted; and
• original history remains reachable through a native recovery ref.

Signed commits in the rewritten range necessarily lose their invalidated
signatures, and this limitation is explicit in the CLI and documentation.

Verification

scripts/validate-skills
  Validated 1 skill(s).

scripts/test
  All 10 tests passed.

The integration suite covers the public help surface, root/linear history,
empty commits, dry-run purity, explicit committers, optional checkpoints, merge
topology, related and excluded ref updates, non-current finish branches,
non-ancestor rejection, dirty-state rejection, invalid refs, and confirmation
requirements.

The repository also passes bash -n, git diff --check, YAML parsing for its
issue forms and workflow, ShellCheck 0.11.0, and shfmt 3.14.0. CI repeats the
shell lint/format checks and runs integration tests on Linux and macOS.

Architectural intent

git-fix-author defines a stable behavior contract, not its forever engine.
Future versions may delegate suitable work to established tools when that
improves correctness or safety without weakening the interface.

Backup lifecycle management remains a focused follow-up rather than expanding
the initial rewrite path.

Closes #1