…0 header

Scans a build output directory for `.map` files and POSTs each to
`/v1/coverage/{repo}/source-maps` so cloud-mode runtime coverage can
resolve bundled paths back to original source files.

Defaults match common CI shape: `--dir dist`, `--include **/*.map`,
exclude `**/node_modules/**`, repo from package.json `repository.url`
or `git remote get-url origin` (trimmed to bare repo name), git SHA
from `$GITHUB_SHA` / `$CI_COMMIT_SHA` / `$COMMIT_SHA` / `git rev-parse
HEAD`. API key is read only from `$FALLOW_API_KEY` to keep the secret
out of argv. Per-map retry on network/`429`/`5xx`, warn at 10 MiB,
reject at 100 MiB. Repo segment is percent-encoded so `owner/repo`
becomes `owner%2Frepo` in the URL.

Exit codes: 0 ok · 1 partial-failure · 2 validation.

Introduces a unified `fallow hooks install|uninstall --target <git|agent>`
command surface so the Git pre-commit hook scaffolder and the Claude /
Codex agent gate share one entry point. `fallow init --hooks` and
`fallow setup-hooks` remain as compatibility aliases that delegate to the
new engine.

The generated Git pre-commit hook now resolves the base ref at commit
time:

    UPSTREAM="$(git rev-parse --abbrev-ref --symbolic-full-name '@{upstream}' ...)"
    if [ -n "$UPSTREAM" ]; then
      BASE="$(git merge-base "$UPSTREAM" HEAD 2>/dev/null || echo "$UPSTREAM")"
    else
      BASE="<fallback>"
    fi
    fallow audit --base "$BASE" --quiet

Diffing against the merge-base with the upstream is the topology-agnostic
answer for repos with multiple long-lived integration branches
(next-release / hotfix / LTS): a feature branch forked off a non-default
integration branch compares against the right fork point, not against
its own remote tracking branch. `--branch` is repurposed as the fallback
used only when no upstream is set.

Includes managed-hook detection via a `# Generated by fallow hooks
install --target git.` marker so `hooks uninstall` preserves
user-authored pre-commit scripts unless `--force` is passed, plus
`--dry-run` for both install and uninstall.

Closes #242