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

docs/cli.md

@@ -36,6 +36,10 @@ vulp <command> [--json] # non-interactive (scripts/AI)
 - **Secret scan**: `sync --action commit-push` refuses to commit staged
   changes that look like credentials (see Git operations); override with
   `--allow-secrets`.
+- **Discord webhook secret**: `vulp digest webhook <url>` stores the URL in
+  `~/.vulp/.tokens` (mode 0600) the same way provider tokens are stored —
+  never in `config.toml`, never printed back, never logged. Whoever has the
+  URL can post to (and edit/delete messages in) that channel.
 - **`VULP_AGENT`** (env var, any non-empty value): every activity-log entry
   written while it's set gets a `· via agent` marker in its detail, so human
   and agent actions are distinguishable in `vulp activity` and the TUI feed.
@@ -139,6 +143,24 @@ review and commit the file yourself. Defaults come from config:
 `default_license` (mit) and `license_holder` (falls back to
 `git config user.name`, then the account username).
 
+## Weekly digest
+
+```
+vulp digest [--json]                    # build + print this week's digest, archive to ~/.vulp/digests/
+vulp digest send discord                # also POST it to the saved Discord webhook
+vulp digest webhook <url>               # store/replace the webhook URL (secret — see Guardrails)
+```
+
+The digest counts only **your own** commits — filtered by `stats_author_emails`
+(config; falls back to `git config user.email`) plus each configured
+account's GitHub no-reply address — not every commit in the workspace
+(most repos here are 90%+ upstream/fork history). It reports: own commits
+this week vs last week, active days, current streak, top 3 repos by own
+commits, local tags created this week, PR/issue open+merged/closed counts
+(provider search API, needs an account), and todos added/done. Every build
+is archived to `~/.vulp/digests/<ISO-week>.md` regardless of `send`.
+`digest send discord` respects global `--dry-run`.
+
 ## Recipes for AI agents
 
 ```bash