feat: add setup did command to publish labeler identity

`cargo run --bin setup -- did` adds #atproto_label and #atproto_labeler to the
DID document via the PDS-signed PLC flow, prompting for the main password and
the emailed code. Splits setup into declare/did modules.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Cargo.lock

@@ -461,6 +461,8 @@ dependencies = [
  "jacquard-axum",
  "k256",
  "rand_core 0.6.4",
+ "reqwest",
+ "rpassword",
  "rusqlite",
  "serde",
  "serde_ipld_dagcbor",
@@ -2847,6 +2849,17 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "rpassword"
+version = "7.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2da316a15f47e3d053de9cb2c439650bd8fa4aaeb9365f2e5f27f492ff73c196"
+dependencies = [
+ "libc",
+ "rtoolbox",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "rsa"
 version = "0.9.10"
@@ -2867,6 +2880,16 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "rtoolbox"
+version = "0.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a1efe12a1469752d0e6ff5ebec0b6ef4924cc5c4c71046b0ec730040535819d"
+dependencies = [
+ "libc",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "rusqlite"
 version = "0.37.0"