Add git-status-report: recursive git repo scanner with status reporting

Scans a directory tree for git repos and produces a concise report
showing uncommitted changes (with +/- character counts) and
ahead/behind status per remote. Supports --dryrun to preview
discovered repos without running checks.

Includes OpenSpec, implementation, and 26-assertion test suite.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/git-status-report.spec.md

@@ -0,0 +1,103 @@
+# git-status-report
+
+## Purpose
+
+Recursively scan a directory tree for git repositories and produce a concise report showing uncommitted changes and remote sync status.
+
+## Usage
+
+```
+git-status-report [OPTIONS] [DIRECTORY]
+```
+
+### Arguments
+
+| Argument | Default | Description |
+|----------|---------|-------------|
+| `DIRECTORY` | `.` (current directory) | Root directory to scan |
+
+### Flags
+
+| Flag | Short | Description |
+|------|-------|-------------|
+| `--dryrun` | `-n` | List discovered repos without running status checks |
+| `--help` | `-h` | Show usage information |
+
+## Behaviour
+
+1. **Discovery phase:** Walk `DIRECTORY` recursively, identifying directories that contain a `.git` folder. Stop descending into a directory once a `.git` is found (don't scan nested repos inside a git worktree).
+
+2. **Status phase:** For each discovered repo:
+   a. Run `git status --porcelain` to detect uncommitted changes (staged, unstaged, untracked).
+   b. For each changed file, compute the character-level diff: `+N` added, `-N` removed. For untracked files, count all characters as `+N`. For deleted files, count all characters as `-N`.
+   c. Run `git remote` to list remotes. For each remote, run `git rev-list --left-right --count <branch>...<remote>/<remote-branch>` to determine ahead/behind counts.
+
+3. **Report phase:** Print a grouped report:
+   - **Clean repos** are listed in a single summary line (count only) unless there are none.
+   - **Dirty repos** get a section each, showing:
+     - Repo path (relative to `DIRECTORY`)
+     - Each changed file with its status and `+N / -N` character counts
+     - Ahead/behind status per remote/branch
+   - **Repos with remote divergence** (ahead or behind) but no local changes still get a section showing the ahead/behind status.
+
+4. **Exit code:**
+   - `0` — all repos clean and in sync
+   - `1` — at least one repo has uncommitted changes or is out of sync
+
+## Dryrun Behaviour
+
+When `--dryrun` is passed:
+- Perform the discovery phase only
+- Print each discovered repo path (relative to `DIRECTORY`), one per line
+- Prefix output with `[dryrun] Would check N repositories:`
+- Do NOT run any git status or remote checks
+- Exit code is always `0`
+
+## Edge Cases
+
+| Scenario | Handling |
+|----------|----------|
+| No git repos found | Print "No git repositories found in <dir>" and exit 0 |
+| Repo has no remotes | Skip remote sync section for that repo, show "(no remotes)" |
+| Repo has detached HEAD | Show branch as `(detached HEAD)` and skip remote comparison |
+| Remote branch doesn't exist | Show "(no upstream)" for that remote |
+| Binary files changed | Show `(binary)` instead of character counts |
+| Permission denied on subdirectory | Skip with warning to stderr, continue scanning |
+| Nested git repos (submodules) | Stop at the outermost `.git` — don't descend further |
+| Symlinked directories | Follow symlinks during discovery |
+
+## Examples
+
+### Clean repos
+```
+Scanned 5 repositories in ~/dev
+
+✓ All 5 repositories are clean and in sync.
+```
+
+### Mixed status
+```
+Scanned 5 repositories in ~/dev
+
+── dirty: project-alpha ──
+  M src/main.py          +42 / -17
+  M README.md            +5 / -0
+  ?? TODO.txt            +120
+  ↕ origin/main: 2 ahead, 0 behind
+
+── dirty: infra-configs ──
+  D old-config.yaml      -89
+  ↕ origin/main: 0 ahead, 3 behind
+
+✓ 3 repositories are clean and in sync.
+```
+
+### Dryrun
+```
+[dryrun] Would check 5 repositories:
+  ~/dev/project-alpha
+  ~/dev/project-beta
+  ~/dev/infra-configs
+  ~/dev/scripts
+  ~/dev/docs
+```