Update docs and prune examples superseded by real functionality

README/certs/README/.env.example/printers.example.toml were all still
describing this as a learning-stage stub with no real printer protocol
clients - rewritten to reflect the real Bambu MQTT client, cert
auto-pinning, and marlin serial connection that now exist.

- Remove examples/fetch_bambu_cert.rs: its manual fetch-and-save workflow
  is now what BambuPrinter::connect()'s ensure_trusted does automatically
  on every connect, so it has no remaining use case.
- Fix examples/printer_polymorphism.rs, which no longer compiled -
  dispatch_gcode was replaced by real methods earlier this session;
  swapped in print_status() as the vendor-only-extension example.
- Remove Config::bambu_ca_cert_overrides/bambu_require_valid_cert and the
  .env vars documenting them - confirmed dead (nothing read them),
  fully superseded by printers.toml's per-printer ca_cert_path/
  require_valid_cert plus automatic trust-on-first-connect pinning.
- Fix stale doc comments in printer/mod.rs and printer/bambu.rs that
  described certificate trust and MQTT as not built yet, or referencing
  the now-removed example.

No behavior change in the daemon itself - verified with cargo build
--examples and a live run of printer_polymorphism and auto_connect_bambu
against the real P1P/H2C printers.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/auto_connect_bambu.rs

@@ -1,12 +1,13 @@
 //! Run with: cargo run --example auto_connect_bambu
 //!
-//! The "smooth, no manual steps" version of test_bambu_certs +
-//! fetch_bambu_cert combined: for each Bambu printer in printers.toml,
-//! makes sure it has a working certificate, auto-pinning one via
-//! trust-on-first-connect if the bundled CA doesn't verify. Safe to run
-//! repeatedly - a printer that's already pinned (certs/pinned/<serial
-//! number>.pem) just gets re-verified against its pin, no network trust
-//! decision is made again.
+//! For each Bambu printer in printers.toml, makes sure it has a working
+//! certificate, auto-pinning one via trust-on-first-connect if the
+//! bundled CA doesn't verify - the exact same `ensure_trusted` step
+//! `BambuPrinter::connect()` runs before opening MQTT, isolated here so
+//! you can check/establish trust without needing a full MQTT handshake to
+//! succeed too. Safe to run repeatedly - a printer that's already pinned
+//! (certs/pinned/<serial number>.pem) just gets re-verified against its
+//! pin, no network trust decision is made again.
 
 use continuum_proxy::fleet;
 use continuum_proxy::printer::PrinterHandle;

examples/fetch_bambu_cert.rs

@@ -1,36 +0,0 @@
-//! Run with: cargo run --example fetch_bambu_cert -- <printer_id> <output_path>
-//!
-//! "Trust on first connect": connects to one printer from printers.toml
-//! with certificate verification disabled, captures whatever certificate
-//! it presents, and saves it as PEM. Meant for a printer like P1P that
-//! doesn't chain to the bundled CA - after running this, point that
-//! printer's `ca_cert_path` in printers.toml at the saved file and
-//! `test_bambu_certs` should report it as verified from then on.
-//!
-//! This trusts whoever answers on the network *right now* - only run it on
-//! a network you trust, ideally right after unboxing the printer.
-
-use continuum_proxy::fleet;
-use continuum_proxy::printer::{GenericPrinter, PrinterHandle};
-
-fn main() -> anyhow::Result<()> {
-    let mut args = std::env::args().skip(1);
-    let printer_id = args.next().ok_or_else(|| anyhow::anyhow!("usage: fetch_bambu_cert <printer_id> <output_path>"))?;
-    let output_path = args.next().ok_or_else(|| anyhow::anyhow!("usage: fetch_bambu_cert <printer_id> <output_path>"))?;
-
-    let printers = fleet::load(std::path::Path::new("printers.toml"))?;
-
-    let pem = printers
-        .iter()
-        .find_map(|printer| match printer {
-            PrinterHandle::Bambu(bambu) if bambu.base().id == printer_id => Some(bambu.fetch_certificate()),
-            _ => None,
-        })
-        .ok_or_else(|| anyhow::anyhow!("no Bambu printer with id '{printer_id}' in printers.toml"))??;
-
-    std::fs::write(&output_path, &pem)?;
-    println!("saved {printer_id}'s certificate to {output_path}");
-    println!("now set ca_cert_path = \"{output_path}\" for {printer_id} in printers.toml");
-
-    Ok(())
-}

examples/printer_polymorphism.rs

@@ -56,9 +56,13 @@ async fn main() {
     // Vendor-only extension: reachable only after matching the concrete
     // variant back out of the enum - one arm now that Bambu is a single
     // type regardless of which protocol version `connect()` settled on.
+    // `print_status()` is real Bambu-only behavior with no equivalent on
+    // `GenericPrinter` (no other vendor here has an in-memory report
+    // cache) - none of these connected above (fake IPs), so it's always
+    // `None`, but the point is the downcast, not a live reading.
     for printer in &fleet {
         match printer {
-            PrinterHandle::Bambu(bambu) => bambu.dispatch_gcode("part.gcode.3mf"),
+            PrinterHandle::Bambu(bambu) => println!("  {}: cached print_status = {:?}", bambu.sn, bambu.print_status().await),
             _ => {}
         }
     }