feat(suppress): group-suppress warnings + ls + journey + docs (M1.5)

- dangling_suppress_warnings takes an ApplyOwner and walks the group's own
  chain (GROUP_CHAIN_LEVELS_CTE) for a group node; runs for both owners.
- GET /groups/{id}/suppressions + `pic suppress ls --group` (client + cmd +
  main.rs; --app/--group mutually exclusive).
- suppress journey: a child group declines a parent template for its subtree;
  suppress ls --group shows the marker. Docs §4.5 + CLAUDE.md move group-level
  suppression from Deferred to implemented.

Completes M1. (An unrelated pre-existing email_inbound dispatch-timing flake
passes in isolation.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/picloud-cli/src/cmds/suppress.rs

@@ -1,18 +1,23 @@
-//! `pic suppress ls --app <a>` — read-only view of an app's §11 tail
-//! per-app opt-outs: the inherited group templates it declines. App-only;
-//! authoring is declarative via the `[suppress]` block (`triggers = [...]`
-//! handler script names, `routes = [...]` paths).
+//! `pic suppress ls --app <a>` / `--group <g>` — read-only view of an owner's
+//! §11 tail opt-outs: the inherited group templates it declines. An app declines
+//! for itself; a group declines for its whole subtree (§11 tail M1). Authoring
+//! is declarative via the `[suppress]` block (`triggers = [...]` handler script
+//! names, `routes = [...]` paths).
 
-use anyhow::Result;
+use anyhow::{bail, Result};
 
 use crate::client::Client;
 use crate::config;
 use crate::output::{OutputMode, Table};
 
-pub async fn ls(app: &str, mode: OutputMode) -> Result<()> {
+pub async fn ls(app: Option<&str>, group: Option<&str>, mode: OutputMode) -> Result<()> {
     let creds = config::resolve()?;
     let client = Client::from_creds(&creds)?;
-    let items = client.suppressions_list(app).await?;
+    let items = match (app, group) {
+        (Some(a), None) => client.suppressions_list(a).await?,
+        (None, Some(g)) => client.group_suppressions_list(g).await?,
+        _ => bail!("provide exactly one of --app or --group"),
+    };
 
     let mut table = Table::new(["kind", "reference"]);
     for s in &items {