Sprint C: author-filtered stats scan, release cadence + repo size, weekly digest

- src/stats/: OwnEmailMatcher (config emails + GH no-reply per account) +
  git-side --author filtering (cheap even on the pterodactyl fork's 4700+
  commits); streak (current/longest, midnight-grace rule), 52-week heatmap,
  day/hour histograms — one scan feeds all of them, data layer only for now
  (visual Stats-tab redesign stays in Sprint D's mockup-first cycle)
- src/stats/cadence.rs: release cadence (median tag gap, local tags, Tier A)
- src/stats/size.rs + cache.rs: git-object vs working-tree size, persisted
  in new ~/.vulp/stats_cache.toml (max 1 sample/day), recorded only during
  [R]/vulp refresh — confirms vulp's own filter-repo cleanup (539MB->834KB)
- src/digest.rs: WeeklyDigest struct + 3 renderers (Discord embed/markdown
  archive/plaintext); vulp digest [send discord|webhook <url>] CLI, webhook
  stored via existing auth token store (~/.vulp/.tokens, 0600), never logged;
  send respects --dry-run
- TUI: [d] on Stats previews the digest in a Modal::Info before anything is
  ever sent
- fix: list_contributors used --all (double-counts after fetching remotes),
  now --branches
- config: stats_author_emails field (TUI-editable)
- verified: streak/delta/top-repo/release math against a hand-built commit
  history, webhook validation+permissions, dry-run, real refresh (51 repos,
  vulp's own entry confirms the filter-repo win), TUI preview via pyte

src/detail/git.rs

@@ -208,10 +208,12 @@ pub fn list_branches(path: &std::path::Path) -> Vec<BranchEntry> {
 
 // ── contributors ─────────────────────────────────────────────────────────────
 
-/// Contributors by commit count across all branches (`git shortlog -sn --all`).
+/// Contributors by commit count across local branches (`git shortlog -sn
+/// --branches`). Deliberately not `--all`: that also counts remote-tracking
+/// refs, so after a fetch every contributor gets double-counted.
 pub fn list_contributors(path: &std::path::Path) -> Vec<ContribEntry> {
     let out = std::process::Command::new("git")
-        .arg("-C").arg(path).args(["shortlog", "-sn", "--all"])
+        .arg("-C").arg(path).args(["shortlog", "-sn", "--branches"])
         .output()
         .unwrap_or_else(|_| std::process::Output {
             status: std::process::ExitStatus::default(), stdout: vec![], stderr: vec![]